Hey MindFlowers68!
That sounds like a classic session timeout or a broken upload cache. When your screen saver kicks in, the browser often "freezes" background processes to save battery, which kills the upload mid-way and can leave your session in a buggy state. Since resetting and re-logging didn't work, try clearing your browser cache or switching to a different browser entirely to see if it bypasses the error. Also, keep your screen active while those high-res photos are sending it’s a pain, but it usually prevents the connection from dropping!
Happy Growing, Growmie!