Not a new system, but just some new code in a lot of places. My guess is that they've got a large number of hard-coded special cases all over the place that have been built up over time and just got a lot worse, when they really need something like a central table of codes and attributes. In my experience in such cases, it can be better to make a big change that requires recoding every case where these things are used than to have a system that mostly works, but fails in numerous subtle ways.

As a customer, the annoying thing is that a lot of errors exist in my flight credits, but I don't know when they'll be finished to the point where it's worth calling them. I've already experienced an extra 600,000 miles in credits that disappeared a couple of weeks later, and I don't even have confidence that changes won't continue to happen months down the line. I believe I'm still missing a number of credits and refunds, but it's hard to reconcile my account with their sketchy histories and continued changes happening.