Hi,
had the same problems twice now (with 2.90 and now with 2.91) ... normally it goes away after switching off and on again, but the first time I had reset and restore my backup. It never happened before with 2.8x, only after the update to 2.90. If I would be performing with unit right now, I would not feel confident!!! Being a software engineer myself I know it is really hard to fix something which is only occurring sporadically ... but pls try anyway :-)
Thanks
Matthias