As mia alluded to, perhaps this is just routine maintenance. However, it seems that, in the past, when other airline credit "loop holes" were closed (e.g. AA gift cards) it often occurred right at the beginning of a new year. I must say if the ability to purchase UA Travel Bank credits with the airline credit goes away, and given the Amex Platinum cards new annual fee of $695, it will be increasingly difficult for me to justify keeping said card...
Regards