Why does my iPhone 15 rotate full screen videos the wrong way?

I am holding it vertically, slightly slanted to try to combat this and this works for a few seconds until it decides to flip upside down again where I have to retry the method until it either settles or stops. I wonder if my phone has a malfunctioning levelling or alignment detection fault. It has been continuing to happen on video players only which is weirdly specific.

As in when in landscape mode, the phone rotates 180 degrees to the wrong orientation. If I wanted it to be landscape and facing me, it rotates the other landscape way and is upside down. It happens in most media players

Yes, it rotates another 180° back to being upside down.