My fat rolls have returned weeks after lipo/BBL. Why did this happen?

The question is where did your surgeon harvest the fat she (or he) used for your BBl?If your surgeon was a board certified plastic surgeon, who has a ton of experience, then you should go back and ask why is this happening. If the back was used as a donor site it's just swelling and it could take months to go away, if the stomach was used and you have gained weight, or even returned to your original weight; the belly bulge is inter abdominal (inside your belly where it can't be reached). Eat multiple small portions, walk an hour every other day, and have patience my dear.

Some rolls are related to skin laxity, and some fullness may be related to swelling. Hard to say without  an exam.  

This really depends on when you had your surgery. If it was fairly recent then the increase in size could be secondary to swelling. You can swell intermittently for months after surgery. If it has been >6 months since your liposuction, then likely the increase in size is from gaining weight. If you don't change your eating habits/exercise routine after liposuction, you will slowly gain that fat back. I would definitely recommend seeing your PS to make sure everything looks okay.