We recently cruised on Regent with flights provided by them. I always download whatever airline app we are flying on. In this case, a code share AA with British Air PHL to Heathrow and Heathrow to Barcelona. Two weeks before the cruise I realized that the Heathrow to Barcelona segment was missing from the app. I called Regent. They had not been informed so they booked us PHL to Madrid and Madrid to Barcelona.
I always think that in this day and age with canceled flights you must investigate your flight arrangements and check every week. We just saw on the AA app that a flight was changed from PHL to Buenos Aires arranged by Regent for January.
Just keep checking your flight arrangements.