I have one XA2 that always underexposes, except for flash shots - they come out perfectly.
I learned 2 things about this XA2
1) Use ONLY Silver-Oxide batteries. Cheap alkalines do not have the strength to hold the shutter open (electro-magnets)
2) Always set the film speed to 1/2 box speed. Meaning set it to 200 for 400 film, 100 for 200 film.
After this, my little XA2 works perfectly.