The raking has to be reasonably even but the 336 is pretty forgiving I find.
Sounds like your auger belt is loose or worn/glazed. Sometimes the pre-compressor tines aren't set right either and lets the hay get away from the pickup teeth at the top.
On the edge of the pickup near the pickup transition to the auger area is hay catching? If it starts to catch there clumps will jam so the auger can't haul it away.