Backups are not clickable/live links?

Something happened in the last week or two and my Tab Outliner opened empty.

I have a number of backups, and I've tried to use those, but the saved trees appear to be just lists of tab names: folders do not open or shut, no links are active. Even if I drag something to my current outline (to try to recover the tabs) changes nothing. They're all just names and lines.

Any help/ideas?

Dianne

(Win10 64, Chrome)