Update: I was using the “SIP” data feed for my requests, but I don’t currently have a paid SIP subscription. Switching to the “IEX” feed made the “split” adjustment work as expected. After digging a little bit deeper, I realized that it’s because SIP has more data, including 00:00:00 - 00:59:59 on 1/13/2022. This one hour, for whatever reason, is unadjusted for the split.
I have the same issue. If it helps, I’ve created a script to identify stocks with a bug in the adjustment, and I’ve identified the following symbols. I hope this is especially useful for those applying ML models.