There is a plastic piece that snaps on the ramp. Make sure you have that. When i first set mine up, i almost threw it out. Without that piece, mine was doing the same.

I have this same issue with my new 40S Ultra. It backs in straight and then hits the back and curves clockwise, multiple attempts and it ends up giving up one foot in front of dock.
Tried:
* problem began when the dock was moved and a new map created.
* careful cleaning of dock and robot
* removing the mop pads
* manually docking
* deleting the old map and creating a new map
* placing robot a meter in front in a straight line with dock and starting Dock sequence.
Getting ready to do a factory reset. Very frustrated.

I am hoping there is an update to the firmware to fix this issue as it does not seem to be uncommon.

Same here. Did all the usual things. This definitely appears to be come kind of software bug.

So, I found that one the back of my x40 ultra, there are two cone shaped holes in the back of the vaccuum. In the bottom of one was a bit of paper towel I think that got stuck there somehow, when I used a toothpick to clean out both cones with some formula 409, it solved the problem of my x40 not being able to self dock that had been happening for months.

Also check the little guide poles that go into those cone shaped holes, they get gunked up and cleaning them helps dramatically

Okay so I finally figured out the problem. Not only was it having a problem docking but I noticed it was slightly tilted and not mopping as well either. I checked out the wheels and sure enough one of them seemed like something was stuck behind the wheel. I pushed the wheel down and rotated it at the same time and after a few rotations a crumbled up balloon came out. It had been behind the wheel for a couple months now. Didn’t prevent the wheel from rotating so it was tricky to figure out what was going on.
It’s docking like normal and mopping great now.