Odoo Enterprise v16

Today I was making a routine blog post and I embedded two images into the text and used one of those also as the header image. The first image uploaded appears fine but the second shows up as a gray camera icon. I tried many things to try to sort this out, including using different images, making a new blog post (in which case any new images failed to show), even rolling back the entire database to last night's backup. As soon as I reconstructed the blog post, the same thing happened. There are no errors pertaining to it in the log (odoo-server.log). All old images continue to be accessed fine and I can even reuse these in further posts and they are fine. The one difference we notice on the embedded images is that all new ones have "?access_token=85e41dae-1847-4302-af4e-65201ac28d31" (or similar number) appended to the end of the file name. It's behaving as though a setting was changed requiring all new images to be accessible only to portal or internal users. As such, they appear fine in the editor, but can't be seen when logged off (gray camera instead). Weird thing is, it only occurs after that "one too many" attachments in the database, right in the middle of a blog edit, so I know that I didn't change any settings.

We verified that the server has plenty of space. I don't know the precise size of ir.attachment, but I can say that I don't have that much stuff in there and none of the files are huge (e.g., most are a few MB, maybe a couple that are 50 MB), maybe a few hundred attachments total.

We noticed in ir.attachment that the new files have "Is public document" turned off, but I have no idea why, nor how to ensure that doesn't keep happening with new uploads.

Does anyone know what this is? Any setting or permission I need to review? Thank you for your time.

Disclaimer: I am not a power user. I understand databases, sql, and I'm fairly experienced with odoo use, but I'm not a python programmer.