Wow! If I had a single shot like this one I would be a raving lunatic. Almost looks like you have light leaking in around the back or something.
Any chance you have occasional focus problems too?
I use a P30+ with AFDII and never seen anything remotely similar to this.
I occasional have problems with metering on manual glass but assumed I got confused on the stop down.
I think the camera is focusing at the right spot, but the back itself hasn't been sharp in the past somehow. A replacement P45 back I had for a while seemed much sharper somehow.
When I had this magenta issue, however, I separated the back from the camera and found a piece of plastic foil over the contact-guard. I removed this, and cleaned the contacts (JR's recommended therapy), haven't had a bad shot since, and sharpness seems improved.
Before buying a back, I did some tests with a Mamiya and P30, and it seemed sharper than my P45+s have been.
I enjoy using the Mamiya as a super-SLR; it would be easier to do if it had the ZD form factor. However, in a few years with live-view we'll probably be able to use the Alpa with back-screen composition and focus. Schneider-MF-compacts, that's what we really need