I posted yesterday about having chain suck off the rear cogs,and today I've recreated the issue and found that randomly I can get the rear cassette totally locked on the rear hub, it wont free spin at all. I have the wheel totally off the bike and no matter how much force I apply in either direction, it won't budge.
The bike, in theory, has a couple hundred miles on it. Ultegra cassette, roval wheel.
Will the wheel still turn on the axle, or is it all jammed solid?
If you've lost the coasting ability but the wheel still turn, then it sounds like it's (one of) the pawls in the clutch mechanism that has fallen out of alignment and is jamming things up. Or possibly a loose adjustment allowing one of the ball bearings to get fouled somewhere in the works.
If it's all jammed solid I'd suspect the wheel bearings instead.
I don't know what kind of freehub body Roval uses. If it's Shimano-style with cup & cone bearings it could be a cone coming unstuck and tightening itself to the point of jamming the wheel.