Hi, I have a drawing with many sheets and many viewports; I have been working on it for some time.
Suddenly all the viewports are not visible and I am unable to see the boundary, stretch or move them.

They are still there; I can double-click inside them and edit the model space.

I can select them using QSELECT

I can add a viewport and it remains visible and editable.

This has happened across all sheets, even ones I rarely access.

It seems there is a global setting I have not found, or cannot access

I have tried deleting the Draftsight Settings file, and using the RECOVER utility, with no result

All other drawings are OK, so seems to be just this drawing

Any help appreciated