Lots of variables here Bill, including the possibility of your
stearated sandpaper leaving residue. This can be a real problem with
some papers, especially if used in a machine.

The craters (fisheyes?) are indeed probably from some contaminate.

I agree with all above, except on one big point:

I only clean my surfaces with a compatible thinner. So paint gets
paint thinner or mineral spirits, shellac calls for anhydrous alcohol,
and lacquer for lacquer thinner.

I found out the hard way that the crap you buy at HD (Kleen Strip,
Crown, etc.) is literally the bottom of the barrel. When having
problems with a finish on exterior doors, I couldn't get the fisheyes
out of the door. I worked, sanded, cleaned, sealed, sprayed,
screamed, pulled out hair, and then called someone that probably sold
the finish on Noah's arc. He switched me over to good quality, non
blended, non recycled lacquer thinner and it fixed it all.

I found out then, there are NO, NONE, ZERO requirements as to
ingredients, purity, processes, strength or anything else when these
guys make their solvents. It is that way for mineral spirits, even
more generic for "paint thinner" (technically anything that thins
paint) and lacquer thinner. That was years ago, and I forgotten all
about it until about a year ago.

I went to a Sherwin Williams open house for industrial coatings and
equipment, I picked up a couple of fives of "Sunnyvale" brand lacquer
thinner for $20 a five as a promo My rep takes me aside to tell me
about this stuff, and says "hey Robert, they have a kick ass deal on
gunwash over at so and so's table. It's the recycled stuff, but it
will still get your guns and equipment clean." And, the Sunnyvale man
cheerfully told me that they are recyclers, and they simply take the
products used in certain manufacturing areas (anywhere from huge
furniture makers to car wreck repair shops) and filter it out, and mix
it to a certain minimum VOC driven formula. His company literally
manufactured nothing. They were well aware that they were considered
"gunwash" and that was just fine with him.

He proudly told me that they tested out with less contaminates than
either Crown or Kleen Strip and proceeded to show me his company's
tests, and asked me if I had ever noticed a difference in the smells/
odor of the Kleen Strip product. I had, and indicated so, and he told
me that odor was dependent on where they got their material (this also
included his product) to start their batching process. I certainly
don't know this to be true, but it made sense. His regional boss was
irritated with him for filling me in with all the details, but it was
a really slow show and it wasn't like he was telling me any trade
secrets.

He rattled off every name you see in HS and Lowes, and told me that
they were all recyclers, and that even though some of them put out
some virgin product, they all recycled and blended to make mineral
spirits, lacquer thinner, and the most blended of all, paint thinner.

His lacquer thinner product did work great for gun cleaning. And to
tell the truth, in moderate weather (70s to about 80) I couldn't tell
any difference when shooting batches of lacquer thinned with it or the
good stuff. But it got squirrelly and a little unpredicatable when
mixing and spraying before and after those temps.

The SW product gives me a much more predictable finish, but it costs
twice as much. For finishing of the really good stuff, I use STARZ
brand lacquer thinner, guys that actually manufacture their own
products. It is expensive, but coupled with a gallon of "gunwash" for
cleaning the price isn't bad..

I would say to clean your surface really well with a clean cloth, and
sand with non stearated (or quality stearated) paper. Clean with a
good lacquer thinner. Thin your lacquer (Deft I go about 10% unless
it is above 85 or so) with a good quality paint store lacquer. Apply.

Save the mineral spirits made from "who knows what and how" for
painted projects.

Robert