Skills randomly changing/resetting

Recently, my skills in Skyrim have been going up and down. Some skills have reset to 15 and others have jumped up to 100 that weren't at 100 before. I made my Pickpocketing skill legendary pretty recently, but that shouldn't cause other skills to change, right?

Restoration was originally at around 50 and it jumped up to 100, but then went down to 90.

Leveling the skills normally doesn't get them back to normal and neither do skill books.

Edit: I'm playing on PC and the only mods I have installed are graphical mods