No issues for the way I shoot (shot)...
1
The X-A1 had no issues (up to a point - meaning almost darkness) in low light. I've shot a variety of still subjects or slow moving subjects in those conditions. Now having said that, although the focus is (was) average for that camera at that time, it is not something you would use for higher speed scenarios. In fact, I may look for another one somewhere because it was such a pleasure to shoot with.
Here are some quick sample images to address your questions/concerns. These photos below were taken several years ago at the Tryon Palace historical area in New Bern, NC (where some of the series "Outlander" was filmed). It was evening, and we went to watch the various colonial Christmas celebrations (it was December). The temps were around 34 F at the time I shot these. NOTE - Except for the first image, most of the scenes were almost dark and lighting was very, very low. Of course, the photos make it look like it was much brighter, which was not the case.
All images shot in Aperture Priority Mode F5 to 6.3 and at various shutter speeds - with ISO's going up to 12,800. Exif data is not present because the batch conversion program that I use is called "Irfanview," which I love to use (it's free) because of all the options available for conversion. The only issue it has is that if you are converting a TIF image to JPG, the exit data is striped (bummer). My work flow involves converting from RAW, then to TIF (my master image format), and then for posting - to medium-sized JPG's.
Image shot at ISO 5000 - f6.3 at 1/30 shutter speed
Image shot at ISO 12,800 - f6.3 at 1/20 shutter speed. Any blurriness is due to movement that couldn't be frozen at 1/20 sec.
Image shot at ISO 12,800 - f6.3 at 1/15 shutter speed. Any blurriness is due to movement that couldn't be frozen at 1/15 sec.
Image shot at ISO 3200 - f6.3 at 1/40 shutter speed. Any blurriness is due to movement that couldn't be frozen at 1/40 sec.
Image shot at ISO 12,800 - f6.3 at 1/10 shutter speed. Any blurriness is due to movement that couldn't be frozen at 1/10 sec.
Image shot at ISO 12,800 - f5 at 1/10 shutter speed. Any blurriness is due to movement that couldn't be frozen at 1/10 sec. Do note that these folks were dancing and moving constantly. It was a recreation of how the slaves (back then) celebrated Christmas - it was a sight to behold, but the scenes were actually much darker than this photo shows (almost pitch dark). Focus was not a problem, but the constant movement of the dancers was difficult to isolate.