I'm going to put my thoughts in this.
For starters, I am struggling with the belt losing or gaining any significance tension when the wheel spins because the sprockets are circles. So assuming the wheel has no change in suspension or is lifted off the ground the tension on the belt should not change. The only thing I can think of off hand is uneven wear which happens on chains I don't know on belts. I just want to point out I am going crazy double checking what I am saying here before I post this and everything I am finding on what you guys are describing is uneven wear or a deeper issue.
As mentioned suspension causes the belt tension to change. A common error which I am guilty of is to tighten a chain or in this case belt on the tight side. Doing so limits suspension travel, even tight within spec. I learned this from my track day experiences. You should keep your belt within spec but towards the looser side, you will be amazed how that will free up your rear suspension. My race bike chains are actually left loose just outside of spec. If you watch slow motion clips of motorcycle racing you can see how loose the chain is because it is waving around all over the place. They have it adjusted to the point where it is just about to fall off, I am not willing to do that.
I do think you need to be careful with an out of spec loose belt on the earlier vrods because it might cause the belt to rub a hole in the tank. I dealt with that issue, but I replaced it with one of those unlimited engineering with a metal guard so I am over that. I don't remember if it was a loose belt or an issue with that tank that cause that.
I agree with all the statements that the rear adjuster cams are uneven. personally I don't know what the hell HD was thinking with that garbage system. There was a time where I considered trying to convert to independent adjusters but then I figured what is the big deal.
The only procedure I know of to change the alignment of the belt or real wheel is to adjust the motor at the front engine mount. This is really changing the angle at which the front sprocket. If there is another procedure I would be very interested to hear it.
On my vrod I can't even put the axle in backwards, I tried that to change the way the wheel aligns.
My guess is to the original problem the belt is too tight.
Here is a simple check for the wheel bearings, works on cars too.
I hope you find this helpful.