Thank you for the clarification on Linphone’s error message!
I made two changes and so far did not have problems yet.
1- Manually set Network Adapter to 100mbits Full Duplex instead of Auto-negotiate
2- In Linphone I disabled “Adaptive rate control”, as there should be plenty bandwidth in my LAN for it, specially with Diffserv enabled with Strict Priority.
I have the logs on to help debugging.
If the problem comes up again I will try Microsip as a softphone to continue the debugging process.
Thanks again for the tip! 