You could reconnect to the onedrive to check if it can work.
And you also could understand the data source according to the article below.
Understand data sources in PowerApps.
I'm having the same issue. The strange thing is that if I try to add an item, it works, despite saying "An error occurred on the server." The addition triggers the appropriate SharePoint workflows and everything, so I can't imagine why it wouldn't be able to populate the list (which it does successfully in the PowerApps editor app).