My concern was that they refused to give me a boarding pass. That caused me to look into it and wondered if there was an equipment swap (there wasn't)

Anyway, it all worked out fine. I flew home on my preselected seat. No SSSS, no issues at the airport. I'm guessing that this was some sort of strange glitch with the app (this was all within 24hr from takeoff, so not the US 24hr rule)