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It's more likely very tiny bubbles of trapped air in the coating resin that were invisible previously but have now been opened and filled with dust from the sanding process which is why they now show up white.
One option is to resand with 320/400 grit, and then apply an extremely light coating of the resin. Don't even use a brush, rather dip a corner of lint-free cloth into the resin and then wipe the surface with that. The aim is to try and build virtually no thickness onto the surface, but hopefully force some resin into those pockets which will fill them. You may find you need to work the resin into the pockets a little bit, and beware of them opening up again afterwards as any further trapped air escapes. If it works, you will have very little work to do and should be able to continue wet-sanding and compounding.
Alternatively, and this is what I would do - don't worry about them. Continue as you were, and then use a release wax (on top of your chemical release agent if you were going down that route) as this will fill them enough to not be a drama.