The store was queried with a [string] but the entity id is a [undefined]

When loading a page in OnPageEdit I first see a warning in the console: 

"Observable store detected, but no sort order specified. You may experience quirks when adding/updating items.  These can be resolved by setting a sort order on the list or grid."

If I try to edit any of the blocks, I get lots of "The store was queried with a [string] but the entity id is a [undefined]" errors.

The error is reported by widgets.js inside Episerver Shell ClientResources folder (version 10.7.1).

Does anybody know what is causing this?