How to resolve "Warning Planning Provider Error" when trying to edit cell that has Line Item Detail?

Summary: Unable to edit existing Planning cell with Line Item Detail. "Warning Planning Provider Error"

Not much more information to provide. When anyone tries to enter a cell that has previously entered Line Item Detail (i.e. right click), the message "Warning Planning Provider Error" appears and the cell cannot be edited. I can enter data for a different account/intersection.

I have confirmed that this is still a level zero intersection and don't believe any other changes have been made. I tried doing a database refresh with validation and that didn't resolve the issue. I believe this was first identified as an issue last week.