New York, NY
I don't think those lines [you mentioned above] are relevant somehow to the setup in question - this is just a "regular" 500 Network Failure, could happen due to many different reasons (this event isn't good by itself, but happens - could be network connectivity issue or even something on our side which prevented the call from progressing properly).
For me it was important to see whether or not 3CX will register to different SBCs or keep sticking to the same one. Seems like the latter. Just tried to find "something" for 3CX that could cause it to move onto another SBC when it's time to re-register.
Well, seems like no luck (one of my hopes was that when only a few records returned - it may behave itself) until 3CX will actually fix their SRV related behavior.