something is wrong with the NPC partner systeme every so often they just start going crazy and swing wildly at nothing and the dont stop until i dismiss them

I have also had this happen
Normally if they have been with me long enough to drop to half health they will start to display this random attack at nothing and not actually attack the bad guys unless you attempt to kite them towards your partner and hope they get a random swing in
Once they start this I just swap out partners. Momotarou seems to be the worst

It's been around since CBT I thought someone would've reported this already?

Oh, it's been reported multiple times. Nothing you can really do about it, it's caused by poor ai/glitches in ai. The only way this would get fixed is if they revamp the ai (heck, I believe the ai has been revamped once already but the issue still remains because more glitches showed up in the programming), but this is a low priority considering that they're not really necessary as a majority of the partners do negligible damage and the only partner I've ever found myself really using at any point (to cheese bosses) is amaterasu and maybe sharo (sheryl).