So seems the issue was NOT a sched change or anything of the sort, but basic tech issues on AA’s side.

Eventually I was able to retrieve the booking. Tried to check in and error. Booking gone again. Tried again several times, and eventually get it again. Ultimately was able to check in and even get boarding passes.

This was on AA.com. Even got it on the app once and was able to get my mobile boarding pass.

My guess: PNR migration from res system to dcs occurred but dcs replication in the cluster was failing or lagging, so depending on where my request was routed, the PNR either existed or didn’t.

thanks for all the suggestions.