On my 360, the debris bag has a nylon strap that goes to a clip on the hose. I don't know if this clip is just to hold the bag upright or if it also helps position the hose - but you can get the clip if yours is lost at most any pool supply store. Polaris 9-100-3135 Bag Tie Collars on Sale at YourPoolHQ
I don't know - but if the bag is hanging off to one side, the weight of the bag with debris in it may cause cleaner to lean to one side and/or track wrong.
I know the water flow is "through the bag" so if the bag is not hanging correctly the water flow could be turning the cleaner (like the jet drive in a boat).
In the manual, if also suggests to remove the head float and shake it to check for water. If there is water, replace the head float. The head float is the white orb attached to the rear of the cleaner body. It also suggests to make sure the hose floats are spaced evenly.
If the float doesn't need to be replaced, I'd check the hoses and make sure you don't have a major leak. I had the same problem and found my supply hose near my unit had cracked, but wasn't noticeable until I got the unit out of the water when it was still running. The crack/expelled water provided enough sideways force to make the unit misbehave.