Thanks everyone. Like I said, I shoot a different XA2 and the XA4 quite regularly, and I know the results I should be getting. I've never had to mess with the 1.5 option. Batteries are fresh, the contacts and sensor are clean. To David's point, there were a few frames where I had to fiddle with the shutter button a bit to get it to engage.
In reviewing my shots, I'm noticing quite a few are underexposed -- not just scenes with a sky. These were all shot on fresh Superia 400, camera set to 400.