I'm having the same problem. Doesn't seem limited to large requests. It does seem to be in Akka though, so maybe it's better if we ask over there?
Akka source
Stack trace:
akka.http.scaladsl.model.
EntityStreamException: Entity stream truncation
akka.http.scaladsl.model.EntityStreamException: Entity stream truncation
akka.http.impl.engine.parsing.HttpMessageParser$$anonfun$1.applyOrElse(HttpMessageParser.scala:320)
akka.http.impl.engine.parsing.HttpMessageParser$$anonfun$1.applyOrElse(HttpMessageParser.scala:318)
akka.stream.impl.fusing.Collect$$anon$2.$anonfun$wrappedPf$1(Ops.scala:212)
akka.stream.impl.fusing.SupervisedGraphStageLogic.withSupervision(Ops.scala:173)
akka.stream.impl.fusing.Collect$$anon$2.onPush(Ops.scala:214)
akka.stream.impl.fusing.GraphInterpreter.processPush(GraphInterpreter.scala:499)
akka.stream.impl.fusing.GraphInterpreter.processEvent(GraphInterpreter.scala:462)
akka.stream.impl.fusing.GraphInterpreter.execute(GraphInterpreter.scala:368)
akka.stream.impl.fusing.GraphInterpreterShell.runBatch(ActorGraphInterpreter.scala:571)
akka.stream.impl.fusing.GraphInterpreterShell$AsyncInput.execute(ActorGraphInterpreter.scala:457)
akka.stream.impl.fusing.GraphInterpreterShell.processEvent(ActorGraphInterpreter.scala:546)
akka.stream.impl.fusing.ActorGraphInterpreter.akka$stream$impl$fusing$ActorGraphInterpreter$$processEvent(ActorGraphInterpreter.scala:725)
akka.stream.impl.fusing.ActorGraphInterpreter$$anonfun$receive$1.applyOrElse(ActorGraphInterpreter.scala:740)
akka.actor.Actor.aroundReceive(Actor.scala:514)
akka.actor.Actor.aroundReceive$(Actor.scala:512)
akka.stream.impl.fusing.<span style="color: rgb(34, 34, 34); font-size: 12.8px; font-style: normal; font-variant-ligatures: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(255, 255, 255)