TrashTerrier I did a restart of the game to no effect. Also tried under WebGL. Same result.
All I can say is that i'm grateful the problem went away as quickly as it did. I have contacted product support on a couple of occasions over one thing or another over the past 5+ years. You can count those on one hand.
I am as perplexed as any. I try to be polite with product support people. They have enough annoyed people to deal with as it is.