So I noticed, that when I'm using the worldedit command //snow in winter in regions with lots of water like beach, river or swamp, there are sometimes small areas where there are layers of sand instead of snow layers. I can't really find a reason why this is happening, as those areas completely change when I undo and redo the //snow command and it does not seem to be related to any biome borders or anything similar.

Report it to them? There's likely nothing we can do about it, because it's likely not being caused by us