SharePoint Add-in Issue

Hi All,

Recently two of our customers have come back with the same issue on their SharePoint Add-in and I fear more are on there way.

All Edit/Display/New aspx pages on all lists (even ones created using standard OOTB) get the below error.

We have implemented a workaround to not use any of these pages and override url's etc. but anyone any idea's what could have caused this? Both clients say no changes have been applied.
Also waiting on MS Dev team contact to come back to us.