second time would be for copying the "updated luma"files to your nand , not necesary anyways, pressing just b will update luma just in your microsd ... I tried updating with x+a from 8.0 directly and it just failed, it's safe.
if you are updating luma to 8.1 from 8.0, I think it copies luma to your nand so it can boot luma without a sd/microsd, you should update pressing b first and then again pressing x+a, or else it will fail
I wouldn't know, I used it when I first bought my console and never again, so I forgot about it, now I checked and it was on... maybe you could check in your banned console if it's on, since you never touched it
there is another share information with nintendo option that should be on this poll, maybe https://gbatemp.net/threads/ban-wave-about-steetpass-mii-plaza.471965/