I was running Pitbull with player, target, tot, focus, focus target. I am using Grid to display raid unit frames.
I disabled Pitbull more than a week ago and deleted the Pitbull configuration file. I also installed ag_UF to replace those unit frames. All freezes have completely disappeared immediately following this change. The problem is 100% gone.
I can recreate the problem again simply by enabling Pitbull, but moving to other unit frame addons definately solves the issue.