This is 120 Acros, shot in a Pentax 645N. I'm fairly sure the camera is not doing this. I had this problem using plastic reels and have switched to a Hewes reel in a stainless tank. I use Ilfosol 3 at the published times (I think it's 5 minutes for Acros). I pour the developer in, start the timer, agitate until about 20 seconds by tipping the tank back and forth at 90 degrees (no rolling or swirling), then tap at an angle and set it down with a thunk (stainless sink). I agitate at each minute by tipping the tank back and forth on an axis (no swirling, etc..) then tap on an angle on two sides and set it down with a thunk. So why on Earth are the edges getting more developed? It's way more obvious on frames that are lighter when printing (like this one). Some that are dark don't show anything.
I know there's enough developer - maybe too much? Don't know if that would cause this.
This is an enlargement on 8x10. The enlarger is also not the problem - I just didn't want to scan the contact print 'cause it'd be too small.