PowerBI app is hanging showing Building your app

Question

We built some reports and published them in a PowerBI app. This all worked fine until recently.

If we go to the app (link https://app.powerbi.com/groups/me/apps/[GUID]), all we see is a spinner "Building your app ..." that never ends.

If we go to a report in the app (link https://app.powerbi.com/groups/me/apps/[GUID]/reports/[ANOTHERGUID], all is fine, the report shows as expected.

We'd like to know what we can do to fix this (already played with licenses and republishing to smaller audience)