Hi Laura,
I used UpdraftPlus for my backup. Backed up into a Google Drive (when Google came back online!!) I haven’t tested the backup by reinstating a backup, just taking it on faith that it would work. 3 Million sites …..
The troublesome plugin was “Responsive Lightbox & Gallery”.
I disabled them all (and I think that the original creator had some installed that are not being used), then went back one at a time activating them. That one was the culprit.
But after updating it, all was OK.
Good luck and stay safe.
Gideon