Here is a thought: Were the images that were missing located in a path like this?
wp-content/cache/2022/07/myfile.jpg
We just discovered this on a legacy site, that a page was missing its images! Caused a mild heart attack.
For whatever reason, rather than using the wp-content/cache/ folder
the FooGallery plugin slaps a cache folder in wp-content.
I do not know if this cache folder is automatically cleared when adding new images or there is a new phase of the moon, but we had to go to the settings of FooGallery to clear it.
wp-admin/edit.php?post_type=foogallery&page=foogallery-settings
Click the aptly named button, Clear Gallery HTML Cache
(assuming you have the “Enable HTML Cache” button checked).
Personally, I think this sort of cache folder should be in wp-content/cache/ and should be flushed when clearing cache-in-general. I mean, that’s what we have this constant WP_CACHE for, right? ??
We also went into Troubleshooting mode, which was somewhat helpful, I heartily recommend using that.