Originally Posted by
McCreed
I can see some of the debris is definitely cloth fibres, and some of the larger lumps look like chunks of dried poly (possibly picked up from the container you're getting the poly out of - eg: the crusty stuff that builds up on the edge of a jar or can). I can't say for sure without being there.
I think you should be able to level that with some sanding now that you're getting a bit build up. I would try maybe some 600 dry, and use a block not just holding the paper in your hand. Light pressure.
The key will be getting nice clean subsequent coats once you have the current coats levelled.
The runs you have around the neck pickup cavity can be removed using the strip sanding technique rather than full block sanding.