My guess is #4,it wouldn't be the first time Harley got a batch of bad wheel bearings. These are sealed bearings and should be good for 100,000 miles. My bike is now at 185,000 miles, I replaced the original bearings front and rear wheels both at 90,000 as a preventative measure only to have them fail on both wheels within 10,000 miles.I'm no expert, but I would be checking the following:
1) Balance - Is the wheel balanced properly? A badly weighted wheel will vibrate and put a lot of stress on the bearings and axle.
2) Grease - The bearings should be swimming in grease, and too much friction can destroy them, so - is there enough grease? Is there somewhere that the grease can escape (damaged gasket or O-ring)?
3) Manufacturing error 1 - Was there an error in manufacturing the axle or rim that is damaging the bearings? Take off the rim, remove the bearings, clean everything and inspect with a magnifying glass...
4) Manufacturing error 2 - Was there an error in manufacturing the bearings causing them to be unusually weak? Did you replace the original bearings with some third-party model that isn't exactly the right size or specification?
If all of these can be eliminated, then you may need professional help to analyse the cause (microscopic inspection of the parts).