I noticed this too, when using the prostitcer - HQ fusion. I asked the HQ instructor about it and her response was "they do that". Didn't care for that answer.
I have always floated my quilt tops. I started measuring from the right side to the side arm, and as I work down the quilt I make sure to keep that straight. Most often I have to pull on it a bit to keep it from being sucked the other way. I think it's from the top being pulled into the batting as it's quilted. It's not much but over 100" it does add up. When using the robotics, you'll be starting on the left and working to the right, so the right side is where you are going to see it.
I also check that I'm staying straight with every advance of the quilt. Since I float, it's super easy to adjust left/right and up/down as needed. I find it's normal that I'll have to ease one side up a bit here and there to keep it straight. I'd be afraid to just keep working down and hoping for the best - I know by how much I adjust that it problably would not be good. It's not a lot, but even easing 1/8" inch for each turn could add up to an inch or more at the bottom. My HQ also likes a loose quilt - I roll it taut, pin and then back off 2-3 notches. This way I keep the back and top the same when I loosen it.
I don't baste at all. I pin the top edge and remove the pins as I go. I pin the sides as I work down.
What I do might sound like a lot of futzing, but it's really not. I can pin load a quilt with backing and be ready to stitch in about 30 minutes (for a queen quilt)