Do you use the most recent version of TBB? Update 2 contains some fixes in the scheduler'sis_out_of_work().
If yes: it supposes we have a race in task priorities implementation which may cause your priority setting to be [temporarly] ignored. Could you please cut a reproducer out from your code and submit it to us? It will greatly help the investigation.
Is there any fixes between theses two updates that could resolve this?
I only got this assertion once while doing heavy stress tests of our applications. I'm not sure I can easily reproduce it. I will do my best to come up with a sample application that raise this assertions.
Meanwhile, if this happens again, that assertion means nothing more than a warning about some temporarily valid but wrong state?