Hello,
I had the exact same problem, and also the "workaround" via Listsettings-Formsettings-Modify Form in PowerApps, did not function. It does now, after many calls with the PowerApps help-service team, although we did not really change anything. Just keep trying, try different browsers, another user log-in, try private window, sometimes it's a cache-data problem.
I also have the issue, that (we use Sharepoint Lists as datasources) some of these lists "copied" themselves but without any content - so on the Site contents, I got the same list name twice, one is the one with data/items, one is empty - no idea why, I or another user did NOT create them, they just appeared by themselves. Very tricky when connecting to datasource, I lost a few nights despairing over functions that should work but did not and finally finding out, they were connected to the wrong "empty" datasource, so nothing to show...
