Working claims from BCBS AZ, anyone else get these letters?

So my office does the billing for over 150 providers, about 50 or so practices ranging in specialty. Nearly all of us have gotten these rejection letters at some point, so the only common denominator I can think of is BCBS AZ is doing something odd behind the scenes. All the rejection will say is the patient name, account #, provider, DOS and dollar amount billed with a note saying “please provide a valid taxonomy code.”

They seem to come from all sorts of plans, FEP, auto forwarded from medicare, primary polices, etc. I even called BCBS AZ today and was asking why this happens, over the course of an hour we compared 4 claims with the same patient over 4 months. No policy change, same provider, same facility, same everything except procedures being billed. Three of the four claims processed and paid, only one rejected. At the end of the call the rep just sort of said, “yeah that’s odd. I’ll try to ask a supervisor and another department for further help.”

Does anyone have any insight into this? There’s no way the taxonomy code is actually incorrect, because no claim would process then lol. This only happens with BCBS AZ, and only to maybe about 5-10% of claims.