Here's a new one for me:

Booked SEA-LAX-GDL for July 13. Roughly 6am departure from SEA, 3pm arrival in GDL
Notice a few days ago that it was now showing a departure of July 12-13 for the flight in the app
Turns out AS moved me to a redeye to LAX leaving the evening before
No notice, no schedule change alert, nothing by email nor any mark on the reservation in the app denoting the schedule had changed
I called and the agent said they don't issue schedule alert changes until 90 days before your flight leaves
I've never heard of that before and know for a fact I've received notices of schedule changes well before 90 days (there's one showing on my app right now for a flight in September)
She moved me back to my original flights, which still existed - she claimed those flights must have been removed from the schedule and later re-added to the schedule at the exact same times as the previous schedule

In the end, it was fixed without issue but only because I noticed it early and called. It's pretty bizarre from my perspective that they would move my flights so dramatically without any notice, but maybe others think this is normal?