I completed the Celestial Tournament the other night and ran into a rather weird bug. After completion, I left the scenario and Mater Li had the gold "!" rather than the "?" he should have. I thought I might be lagging so I ran around a bit and then realized it was not lag.
I did the usual thing one does when one encounters a turn-in bug (and when it's too troublesome to abandon and restart the quest chain), I logged out & restarted. When I logged back in, the completed quest was completely missing from my quest log. After a few choice phrases better left to the imagination, I retook the quest, reentered the tournament, and completed it a second time. Upon exiting... same thing: Mater Li had the gold "!" rather than the "?" he should have.
Knowing if I camped out, I would likely lose completion credit again, I placed a support ticket for the bug (knowing it would be 24 hours before a GM would pay any attention to it) and proceeded to try other options to fix it.
I tried phase-hopping to another server... still no "?" I tried leaving the immediate area ... still no "?" I tried leaving the continent and then returning... still no "?" I tried hearthing to garrison and then returning... still no "?" I tried logging to an alt, and then trying the turn in with a different character than the one that completed the quest... still no "?". Firmly irritated and not willing to give up my completion, I tabbed out and discovered this has been a recurring bug since 2014 (reports in forums going back as far as May). The general consensus is that no one knows what causes it and it's a crapshoot if logging out and back in will actually fix it or completely remove your quest from your log. The only advice given in the forums was to go to Orgrimmar (or Stormwind if Alliance) specifically before logging out and back in (not sure why these specific locations would fix the situation).
I am largely posting this just to let people who encounter it know you are not alone. If anyone knows a way to reliably get past this bug, I would appreciate learning of a fix.