Image links partly broken after WP5.5

Our church site has some image problems since WordPress 5.5. I removed an old media folder plugin and that solved many problems. The URL I provided here is an example. The topmost image of the building exterior had been replaced by an empty box. The file definitely still on the server. When I went into the page editor (Classic not blocks), and deleted the existing image link, and used Add Media tool, the Add Media gallery showed a significant number of blank pale gray boxes instead of image thumbnails. Anyway, on going through the Add Media (insert image) process, it showed up on the page again. But, two on my example page here are still missing (ran out of time).

Really puzzled. Some way to clean this up? Some tool?

The page I need help with: [log in to see the link]