Recalls 1 and 3 describe the same underlying driveshaft/axle defect. Recalls 2 and 4 describe the same airbag sensor defect. So there are really 2 distinct issues, but 4 total recall filings.
The 2021 Acura RDX has 4 recalls, the most serious being a front driveshaft that can fail without warning, cutting drive power to the wheels or allowing the vehicle to roll away if parked without the parking brake applied.
The other recall involves the front passenger seat sensor, which detects whether the seat is occupied by an adult. If the sensor misreads the occupancy, the passenger airbag can deploy unexpectedly during a crash rather than in the way intended, raising the risk of injury to whoever is in that seat.