Unable to view/edit certain pages after database restoration

I’m having a peculiar and frustrating problem: If I restore my site database from backup, certain pages appear blank and empty when viewed in the Classic Editor. Each affected page retains its title, slug, and metadata, but the Classic Editor interface shows the actual content as completely blank in both Visual and Text views and the word count display shows 0.

The content of those pages is still present in the post_content fields in the posts table in the database, and the pages load normally if accessed from the front end.

If I deactivate Classic Editor and reopen an affected page in the Gutenberg block editor, I can view and edit the existing content. However, if I switch back to Classic Editor, that content seemingly disappears again.

(The same behavior occurs if I use the Disable Gutenberg plugin rather than Classic Editor to disable the block editor.)

This appears to happen only to pages, and not to all of them. I can identify no common factors among the affected pages other than that they are pages (not posts).

The only way I have found to reenable editing in the Classic Editor is to copy the HTML for each affected page, paste it into the HTML view in the editor, and resave, which must be done for each affected page. Running another database restoration will recreate the problem, requiring each page’s content to be replaced again in the same manner.

The problem happened on multiple sites running different themes, so it doesn’t appear to be theme-related. The database backup files seem to contain the correct data, and neither the backup nor the restore operations return serious errors. However, this weird effect is now happening every time.

I was previously able to run restore operations without issue, through at least WordPress 5.5.1. (I had run a restore on October 23, a few days prior to the 5.5.2 update, which did NOT create this problem.) I have no idea what would cause certain pages to suddenly become uneditable using the Classic Editor, but still editable via Gutenberg.

If you have any idea what might be happening, I would welcome your input. I’m baffled!