Looking at published data, American is approaching 500 flight cancellations over the course of a four day period around this weekend:

• On Friday, June 18, 2021, American canceled 83 flights
• On Saturday, June 19, 2021, American canceled 123 flights
• On Sunday, June 20, 2021, American canceled 167 flights
• On Monday, June 21, 2021, American canceled 97 flights

There are two different reasons being given for flight cancellations, including “flight crew unavailable” and “operational decisions.” That suggests that these cancellations are likely related to American not having enough staff. And then for cancellations due to “operational decisions,” presumably that’s for situations where American prioritized one flight over another (which happens due to a variety of factors).

The cancellations seem to primarily be focused on the Boeing 737 fleet, which suggests that the crewing issues are related to pilots rather than flight attendants (since pilots are rated on a specific type of aircraft, while flight attendants are generally trained on all mainline aircraft).