When I used the 5" single speed Porter Cable RO sander, the epoxy on the deck which I was sanding seemed to "ball up" a bit. This didn't happen when I switched to my 6" RO (same grit) with the variable speed dialed down.

I suspect that the main issue was that the epoxy was still a bit green and the much higher speed of the single speed generated greater friction/heat which further softened the epoxy and caused the problems. Now that I have two RO sanders, I have not experienced the problem again.

FWIW, for further dust reduction, you can rig a partially filled 5 gallon pail of water in-line between the sander and the vacuum. Most of the dust and debris will wind up being trapped in the water in the pail rather than clogging your vacuum filter.