I recently added a bunch of old diaries and had abotu 1 in 20 uploads fail. I noticed it was on pictures that required more processing / resizing effort (slower process than other files).
So, if it's a super high resolution and minimal compression, it might make it fail more often? While you might want to keep high reso / large file sized files for your own record, you might want to run a programs to slim them down before uploading and see if that works better. if it does, some programs can repeat the same process on a batch of files and it can be as simple as pressing a button, saving them to a predetermined location of your choice ready for upload. keep your good files, delete the uploaded ones when done.
test a single file before investing the efffort.