This was on a clean 14.04 machine where I had not touched anything kurento-related before so the problem is not related to any prior installation or old remains of that.
0:00:07.696440027 15356 0x10426d0 INFO KurentoMediaServer /build/buildd/kurento-media-server-5.0.2/server/main.cpp:183:main: Kmsc version: 5.0.2
0:00:07.696565542 15356 0x10426d0 INFO KurentoMediaServer /build/buildd/kurento-media-server-5.0.2/server/main.cpp:66:load_config: Reading configuration from: /etc/kurento/kurento.conf.json
0:00:07.720167656 15356 0x10426d0 INFO KurentoMediaServer /build/buildd/kurento-media-server-5.0.2/server/main.cpp:73:load_config: Configuration loaded successfully
0:00:07.720338435 15356 0x10426d0 INFO KurentoModuleManager /build/buildd/kms-core-5.0.3/src/server/implementation/ModuleManager.cpp:99:loadModules: Looking for modules in /usr/lib/x86_64-linux-gnu/kurento/modules
0:00:08.028144088 15356 0x10426d0 INFO KurentoModuleManager /build/buildd/kms-core-5.0.3/src/server/implementation/ModuleManager.cpp:74:loadModule: Module /usr/lib/x86_64-linux-gnu/kurento/modules/libkmselementsmodule.so loaded
0:00:08.028999213 15356 0x10426d0 INFO KurentoModuleManager /build/buildd/kms-core-5.0.3/src/server/implementation/ModuleManager.cpp:74:loadModule: Module /usr/lib/x86_64-linux-gnu/kurento/modules/libkmsfiltersmodule.so loaded
0:00:08.029262746 15356 0x10426d0 INFO KurentoModuleManager /build/buildd/kms-core-5.0.3/src/server/implementation/ModuleManager.cpp:74:loadModule: Module /usr/lib/x86_64-linux-gnu/kurento/modules/libkmscoremodule.so loaded
0:00:08.099068622 15356 0x10426d0 INFO KurentoWebSocketTransport /build/buildd/kurento-media-server-5.0.2/server/transport/websocket/WebSocketTransport.cpp:197:WebSocketTransport: Secure websocket server not enabled
0:00:08.099478582 15356 0x10426d0 INFO KurentoMediaServer /build/buildd/kurento-media-server-5.0.2/server/main.cpp:194:main: Mediaserver started
0:06:24.133985603 15356 0x10bd980 DEBUG KurentoWebSocketTransport /build/buildd/kurento-media-server-5.0.2/server/transport/websocket/WebSocketTransport.cpp:458:openHandler: Client connected from
0:06:24.227529401 15356 0x7f9520002520 DEBUG KurentoWebSocketTransport /build/buildd/kurento-media-server-5.0.2/server/transport/websocket/WebSocketTransport.cpp:437:processMessage: Message: >{"id":1,"method":"create","params":{"type":"MediaPipeline","constructorParams":{}},"jsonrpc":"2.0"}<
0:06:24.233666315 15356 0x7f9520002520 DEBUG KurentoServerMethods /build/buildd/kurento-media-server-5.0.2/server/ServerMethods.cpp:193:postProcess: Caching: {"id":1,"jsonrpc":"2.0","result":{"sessionId":"861f1ea9-9c39-4399-86f9-249814d9a6d0","value":"74e2eaaf-a743-4185-8fba-5522917d483f"}}
0:06:24.233909894 15356 0x7f9520002520 DEBUG KurentoWebSocketTransport /build/buildd/kurento-media-server-5.0.2/server/transport/websocket/WebSocketTransport.cpp:439:processMessage: Response: >{"id":1,"jsonrpc":"2.0","result":{"sessionId":"861f1ea9-9c39-4399-86f9-249814d9a6d0","value":"74e2eaaf-a743-4185-8fba-5522917d483f"}}
<
0:06:24.233994970 15356 0x7f9520002520 DEBUG KurentoWebSocketTransport /build/buildd/kurento-media-server-5.0.2/server/transport/websocket/WebSocketTransport.cpp:391:storeConnection: Asociating session 861f1ea9-9c39-4399-86f9-249814d9a6d0
0:06:24.306129841 15356 0x10bd980 WARN KurentoWebSocketTransport /build/buildd/kurento-media-server-5.0.2/server/transport/websocket/WebSocketTransport.cpp:297:injectSessionId: Injecting sessionId 861f1ea9-9c39-4399-86f9-249814d9a6d0
0:06:24.306270595 15356 0x10bd980 DEBUG KurentoWebSocketTransport /build/buildd/kurento-media-server-5.0.2/server/transport/websocket/WebSocketTransport.cpp:437:processMessage: Message: >{"id":2,"jsonrpc":"2.0","method":"create","params":{"constructorParams":{"mediaPipeline":"74e2eaaf-a743-4185-8fba-5522917d483f"},"sessionId":"861f1ea9-9c39-4399-86f9-249814d9a6d0","type":"WebRtcEndpoint"}}
<
0:06:24.307980296 15356 0x10bd980 DEBUG KurentoServerMethods /build/buildd/kurento-media-server-5.0.2/server/ServerMethods.cpp:193:postProcess: Caching: {"error":{"code":-32000,"data":{"code":40107,"message":"Cannot create gstreamer element: webrtcendpoint"},"message":"Cannot create gstreamer element: webrtcendpoint"},"id":2,"jsonrpc":"2.0"}
0:06:24.308166214 15356 0x10bd980 DEBUG KurentoWebSocketTransport /build/buildd/kurento-media-server-5.0.2/server/transport/websocket/WebSocketTransport.cpp:439:processMessage: Response: >{"error":{"code":-32000,"data":{"code":40107,"message":"Cannot create gstreamer element: webrtcendpoint"},"message":"Cannot create gstreamer element: webrtcendpoint"},"id":2,"jsonrpc":"2.0"}
<
0:07:08.115937974 15356 0x7f9518001cc0 INFO KurentoWebSocketTransport /build/buildd/kurento-media-server-5.0.2/server/transport/websocket/WebSocketTransport.cpp:227:keepAliveSessions: Keep alive 861f1ea9-9c39-4399-86f9-249814d9a6d0
0:08:08.126603471 15356 0x7f9518001cc0 INFO KurentoWebSocketTransport /build/buildd/kurento-media-server-5.0.2/server/transport/websocket/WebSocketTransport.cpp:227:keepAliveSessions: Keep alive 861f1ea9-9c39-4399-86f9-249814d9a6d0
0:09:08.126935643 15356 0x7f9518001cc0 INFO KurentoWebSocketTransport /build/buildd/kurento-media-server-5.0.2/server/transport/websocket/WebSocketTransport.cpp:227:keepAliveSessions: Keep alive 861f1ea9-9c39-4399-86f9-249814d9a6d0
0:10:08.127617524 15356 0x7f9518001cc0 INFO KurentoWebSocketTransport /build/buildd/kurento-media-server-5.0.2/server/transport/websocket/WebSocketTransport.cpp:227:keepAliveSessions: Keep alive 861f1ea9-9c39-4399-86f9-249814d9a6d0
0:10:24.235720242 15356 0x7f951c001a70 DEBUG KurentoMediaSet /build/buildd/kms-core-5.0.3/src/server/implementation/MediaSet.cpp:65:doGarbageCollection: Running garbage collector
0:11:08.128044471 15356 0x7f9518001cc0 INFO KurentoWebSocketTransport /build/buildd/kurento-media-server-5.0.2/server/transport/websocket/WebSocketTransport.cpp:227:keepAliveSessions: Keep alive 861f1ea9-9c39-4399-86f9-249814d9a6d0
0:12:08.128377322 15356 0x7f9518001cc0 INFO KurentoWebSocketTransport /build/buildd/kurento-media-server-5.0.2/server/transport/websocket/WebSocketTransport.cpp:227:keepAliveSessions: Keep alive 861f1ea9-9c39-4399-86f9-249814d9a6d0
0:13:08.129768214 15356 0x7f9518001cc0 INFO KurentoWebSocketTransport /build/buildd/kurento-media-server-5.0.2/server/transport/websocket/WebSocketTransport.cpp:227:keepAliveSessions: Keep alive 861f1ea9-9c39-4399-86f9-249814d9a6d0
0:13:55.674481992 15356 0x7f9520002520 DEBUG KurentoWebSocketTransport /build/buildd/kurento-media-server-5.0.2/server/transport/websocket/WebSocketTransport.cpp:497:closeHandler: Connection closed
0:13:55.674544247 15356 0x7f9520002520 DEBUG KurentoWebSocketTransport /build/buildd/kurento-media-server-5.0.2/server/transport/websocket/WebSocketTransport.cpp:503:closeHandler: Erasing connection associated with: 861f1ea9-9c39-4399-86f9-249814d9a6d0
0:14:24.236481705 15356 0x7f951c001a70 DEBUG KurentoMediaSet /build/buildd/kms-core-5.0.3/src/server/implementation/MediaSet.cpp:65:doGarbageCollection: Running garbage collector
0:18:24.236846785 15356 0x7f951c001a70 DEBUG KurentoMediaSet /build/buildd/kms-core-5.0.3/src/server/implementation/MediaSet.cpp:65:doGarbageCollection: Running garbage collector
0:18:24.236934019 15356 0x7f951c001a70 WARN KurentoMediaSet /build/buildd/kms-core-5.0.3/src/server/implementation/MediaSet.cpp:73:doGarbageCollection: Session timeout: 861f1ea9-9c39-4399-86f9-249814d9a6d0
0:18:24.237039542 15356 0x7f951c001a70 DEBUG KurentoMediaSet /build/buildd/kms-core-5.0.3/src/server/implementation/MediaSet.cpp:358:releasePointer: Destroying MediaPipeline -> 74e2eaaf-a743-4185-8fba-5522917d483f
0:22:24.238516608 15356 0x7f951c001a70 DEBUG KurentoMediaSet /build/buildd/kms-core-5.0.3/src/server/implementation/MediaSet.cpp:65:doGarbageCollection: Running garbage collector
0:26:24.239240429 15356 0x7f951c001a70 DEBUG KurentoMediaSet /build/buildd/kms-core-5.0.3/src/server/implementation/MediaSet.cpp:65:doGarbageCollection: Running garbage collector
0:30:24.240469300 15356 0x7f951c001a70 DEBUG KurentoMediaSet /build/buildd/kms-core-5.0.3/src/server/implementation/MediaSet.cpp:65:doGarbageCollection: Running garbage collector
0:34:24.241624818 15356 0x7f951c001a70 DEBUG KurentoMediaSet /build/buildd/kms-core-5.0.3/src/server/implementation/MediaSet.cpp:65:doGarbageCollection: Running garbage collector
0:38:24.242728586 15356 0x7f951c001a70 DEBUG KurentoMediaSet /build/buildd/kms-core-5.0.3/src/server/implementation/MediaSet.cpp:65:doGarbageCollection: Running garbage collector
0:42:24.244320596 15356 0x7f951c001a70 DEBUG KurentoMediaSet /build/buildd/kms-core-5.0.3/src/server/implementation/MediaSet.cpp:65:doGarbageCollection: Running garbage collector
0:46:24.245066150 15356 0x7f951c001a70 DEBUG KurentoMediaSet /build/buildd/kms-core-5.0.3/src/server/implementation/MediaSet.cpp:65:doGarbageCollection: Running garbage collector
0:50:24.245358033 15356 0x7f951c001a70 DEBUG KurentoMediaSet /build/buildd/kms-core-5.0.3/src/server/implementation/MediaSet.cpp:65:doGarbageCollection: Running garbage collector
0:54:24.247508526 15356 0x7f951c001a70 DEBUG KurentoMediaSet /build/buildd/kms-core-5.0.3/src/server/implementation/MediaSet.cpp:65:doGarbageCollection: Running garbage collector
0:58:24.248789308 15356 0x7f951c001a70 DEBUG KurentoMediaSet /build/buildd/kms-core-5.0.3/src/server/implementation/MediaSet.cpp:65:doGarbageCollection: Running garbage collector
1:02:24.250458830 15356 0x7f951c001a70 DEBUG KurentoMediaSet /build/buildd/kms-core-5.0.3/src/server/implementation/MediaSet.cpp:65:doGarbageCollection: Running garbage collector
1:06:24.250843507 15356 0x7f951c001a70 DEBUG KurentoMediaSet /build/buildd/kms-core-5.0.3/src/server/implementation/MediaSet.cpp:65:doGarbageCollection: Running garbage collector
1:10:24.251450819 15356 0x7f951c001a70 DEBUG KurentoMediaSet /build/buildd/kms-core-5.0.3/src/server/implementation/MediaSet.cpp:65:doGarbageCollection: Running garbage collector