25 mb is the limit on the file size. the unlimited uploads isn't the size of the file its how many files you can send. the basic account allows only 25 images total. the paid for is as many as you want.
as for why you can't send more i don't know. if the file is too large it will say its too large. since you have only 9 images, i would say its your file size.
It's, just a guess, but it sounds like FAA is not liking your photo files. Try opening them with whatever software you use and resave them as a standard jpeg. If that doesn't work, download something like IrfanView (it's free), and open and resave the files as jpgs and then give the uploads another try.
i assume your saving them as jpg, and not just naming them jpg? are you sending it from a phone? try a different browser. it could be that or a malware type blocker you have preventing you from doing more.
also, while i doubt this has to do with uploading (you never know), upload an avatar. maybe there is a new thing in the system that prevents uploads if you don't have one? just a wild guess.
If you are using an iPhone (or some Androids) you may be trying to upload HEIF files and FAA won't accept them.
You need to convert them and switch your settings to save to jpg so you won't have the problem in the future. I suppose it's possible if you are doing digital edits on your phone those saves are being converted to jpg so they work.