I received a reply to my email.
Hi Steve:
I hope you're doing well!
We have seen this before, and it definitely appears to be post-BEP. Your hunch of environmental damage seems consistent with my way of thinking. Whether it was a thermal or chemical reaction, I could only begin to guess by looking at a picture. Either way, I wouldn't be thinking of adding these to your error collection!
Wishing you a safe and happy New Year!