I will note for the forum here on FT that last year around this time the same situation appeared to have occurred. Credits for the UA TB were taking longer than usual and people reported this notion of it being "patched" by AMEX. It turned out that the code they use was just backed up and being updated. Credits posted a few weeks later.
Didn't the issue last year include ALL Amex credits (ie. I remember my wireless credit being delayed)? This year seems very specific to United TB. Someone even mentioned they received a baggage credit as expected for a post 2/5 charge. The situation definitely feels different this year.