Yes, I have tried a couple of times to do dugi fix to make this go away. The only way I have found to reliably make this error go away once it happens is to keep questing, and it will go away at some point when picking up a new quest, quest item, quest giving item, or quest turn-in.

Reloading, relaunching etc. does not make it go away.

Is there anything in particular I can do next time I see this to help track it down?

I do also get that last traceback (the non-repeating one) rather more often, but it does not actually impact the use of the addon since dismissing it just … makes it go away. But could be related, obviously.