iTunes keeps losing media (making mp3s unplayable) please help

I have the newest iTunes and ios, so I dont know if that is the problem.. I've tried adding all the songs to my iTunes library (instead of just dragging when my phone is connected), reinstalling iTunes, deleting all the unplayable songs and re-adding, using iTunes in safe mode etc.. I have a tonne of space left on my phone, why does this keep happening? It's frusturating losing over a thousand songs for no reason I can figure out lol. Also, I don't delete the music from my computer files, they stay in the same place.