I had booked (with BA on BA ticket) a flight from LHR-MIA and returning to LHR from JFK. Originally I booked to leave tomorrow (Saturday) on an AA and returning on a BA flight from New York. My return flight was cancelled, and I was given the option to rebook the whole itinerary, so I changed my outbound flight to Sunday and chose a different flight on the same day for the return.

Everything looks fine on MMB on BA.com for my new flight on Sunday after the change.

But just now, I got an email asking me to check-in to the Saturday AA flight from AA! It had a different AA record locator and is showing ticketed (but the return is not on the AA booking). I tried to call BA, but got the "we are busy and are not picking up right now" message. Do I need to worry that they will cancel the whole itinerary when I don't show up for the AA flight? Or is this a common error that I can just ignore?