What you have there is a phenomenon called "Corning". It is caused by (or a combination of) soft (uncured) material, too fine of a grit, wrong sanding pattern (of the machine)
That soft material could also be a very thick (multiple layers) of an old oil-based paint.
The fine grit is self-explanatory.
The pattern is the sander itself. A small-orbit DA type sander is really intended for finish sanding, just throwing a coarse grit paper on it will not do the same as it would on the correct sander.
Swapping to a geared-orbital sander will be much more aggressive. The idea is to scrape that paint out of there without re-grinding it into the rest of it. That creates heat, which glues those globs back together.
Lastly, a pure spinning machine, like a grinder with the appropriate sanding pad, often works well too.
A lot of this depends upon the size of the area you are sanding/stripping.
I have literally stripped an entire pickup truck of years worth of enamel paint, with a 7" sander/polisher, but that is probably overkill for smaller projects.
The RAS 115 would be ideal for this, but they are sadly discontinued. There are alternatives still available though.
Next choice would be a Rotex, size depending on the project.
There are also variations in abrasives. Look for one with the intent of stripping. These are usually "Stearate" coated. This is a soap-like material that lubricates, which keeps the swarf from sticking/balling up.....corning.
Sometimes this will be a slightly different grit. Say your typical 40 grit is "open coat", the closest Stearated version might be 36 grit.
None of this is guaranteed, just check for the coating. That type of paper will perform better, no matter the grit, but they quit doing it at a certain point.
