I'm using a Gates Belt drive CDX setup with a Shimano Alfine 8 hub on a SOMA Wolverine frame. Over about 6000 km, I've worn out 3 stainless steel rear sprockets; the last one lasted only about 600km. The small protrusions that are supposed to hold the sprocket fixed on the axle look like they have been completely filed away, and the sprocket just spins freely on the axle. Also, for two of the three broken sprockets, there was a small crack in one of the 'arms' that center the sprocket on the axle. The corresponding surfaces on the axles (I also exchanged the hub once along the way) don't seem to have any abnormal wear on them.
I realized now that the chainline on the bike isn't perfect (front is about 45mm, back is 43.7, where Gates say +/- 1mm is ok). The bike is mostly ridden in the city, not always in perfect conditions but not terribly muddy either.
Before I invest in another rear sprocket, any idea about what I can do to prevent this from happening again.