Trying to run e.g. qmlbench fails due to QQmlThread not starting. After reverting qtbase to 5.10 threads run again. In corelib/thread there are several commits for thread optimization that are the most like culprit. I could try reverting them one by one to see which one. I do think it is on top of the stack though as I used dev version from few weeks back and then the threads still started.

Problem is that this environment is not easily available and BSP is somewhat unstable so is it the platform thread scheduling that is the real thing to blame or the new optimizations. Could be interesting to see how this behaves on QNX.