Maybe that helps:
jacktrip -S --loopback 
mThreadPool default maxThreadCount = 2 
mThreadPool maxThreadCount previously set to 32 
JackTrip HUB SERVER: UDP Base Port set to 61002 
JackTrip HUB SERVER: Waiting for client connections... 
JackTrip HUB SERVER: Hub auto audio patch setting = 0 (server-to-clients)
======================================================= 
JackTrip HUB SERVER: Client Connection Received! 
JackTrip HUB SERVER: Client Connect Received from Address : ::ffff:84.175.232.149 
JackTrip HUB SERVER: Reading UDP port from Client... 
JackTrip HUB SERVER: Client UDP Port is = 4464 
JackTrip HUB SERVER: Sending Final UDP Port to Client: 61002 
Writing port: 61002
JackTrip HUB SERVER: Client TCP Connection Closed! 
JackTrip HUB SERVER: Starting JackTripWorker... 
Segmentation fault (core dumped)