US airlines are notorious for schedule changes, particularly for the new autumn and spring timetable periods.
I almost always buy my US flights direct from the airline for this reason, either revenue or award. Far more flexibility this way because things like married segments don’t matter as they reaccommodate you.
I’ll still use QFFF to connect a US domestic flight to an international gateway. Usually that’s ok in terms of flexibility if it’s a single segment. Sometimes this works to your advantage too when the only award seat might initially be at an inconvenient time, but once the schedule change kicks in you can move it to the new - better timed - flight