So... I also ended up doing a factory data reset. I spent a lot of time over the past 5 days trying to resolve the issues without doing the reset, but I think this actually saves me time in the long run and gives me closure.
I have the same issue, which started about about 4 days ago. I have a Note 8. I cannot edit, delete, send/attach any photos regardless of whether they are saved internally or externally. I can delete files through My Files, but that's it.