I seriously doubt it has anything to do with the film itself being a tiny bit past date. In fact, Acros II has been around only briefly. I've shot original Acros 20 years past date, not even frozen beforehand, with complete success - (not that I recommend doing that). And I've processed older120 roll Acros thawed out after a number of years with zero issues. Perhaps there was some crud clinging to the walls of the processing drum, which broke free during processing and contaminated things. Clean your drum and reel well, try another developer, and see what happens. And use the lowest RPM your processor will allow. Does the developer get frothy, the way you do it?
The other possibility is that, being finished by Harman now, rather than Fuji, some of their own defective backing paper was involved. You'd have to inquire about that.