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I found by accident that I could remove most of these lumps of melted finish that clog sandpaper by swiping my sanding block across the carpet on top of my work bench. One pass and most of them are gone. It was an epiphany.

Also found that all sandpaper is not created equal in regard to clogging. My last project I splurged on the expensive stuff at the hardware store. Clogging reduced by 3/4 as compared to wet/dry sandpaper. My local hardware store is a True Value affiliate, perhaps its selection of sandpaper is available nationally.

The rattle-cans of Zinsser shellac that I have are identified as wax-free, which lets me lay down an even seal coat. I need all the protection from myself that I can get.

I've found, as somebody already said, shellac takes longer to completely harden up that one might think. It may he "dry" in a few hours, but it may take a week or more to get really hard. I suspect the same may be true of lacquer, and if one builds up too much thickness too fast it may do weird things.

In the “old days” custom car builders would let their cars with lacquer based primer dry for months before sanding to account for the shrinkage. (modern epoxy type primers hardly shrink)

yeah not all shellacs are the same. I think 12 hrs should be fine but I only use
flake shellac and everclear I make my own