v3 to v4 hidden addons

I have encountered a problem on a site that was originally built in SPPB3 and subsequently converted to SPPB4. I have a couple of pages where I had some Text Block addons that were hidden in SPPB3. Now in SPPB4 these hidden addons are uneditable which means I can neither unhide them or delete them - if you hover over them there is just a "no-entry" cursor, and neither right- nor left-clicking makes any difference. Ideally I would like to at least be able to delete these items if they can't be restored/unhidden.
This seems to only apply to addons in columns, as complete rows that were hidden appear to be restorable.
https://www.theoministries.com you will see this clearly on Retreats page, but also occurs on some others.