[THE ISSUE IS FIXED NOW - Turns out I was the problem, all I had to do was disable one large app, and now everything is backing up properly again.. Thanks everyone for an answer, I appreciate it.]
Recently I've run into some issues with iCloud, I'll explain:
Yesterday I cleaned up some space on my iPhone, since I kept on getting bothered by my phone constantly telling me to upgrade my iCloud storage. I freed up about 10gb, but somehow still couldn't sync my photos.
I've tried restarting both my iPad and my iPhone, emptying my bin on about every single app, and even decided to delete my backups, but when I saw that even having 10 out of 50gb won't fix the issue, I backed up my devices again, and sure enough my iPhone had been backed up successfully, but my iPad was not, since apparently I don't have enough space.