Found a new-ish solution today: Republishing the layer that is in use.
I tried steps 1 and 2. This does work some days, but not today. (AR Invoice Entry is just evil.)
I opened the app without a layer - I did this by deleting that portion of the URL (highlighted below). It opened fine. This tells me that the layer is the issue.
So then I opened App Studio to the layer and republished it, and that worked. No log-out needed.
With layer
Without layer
