This will sound silly, but don't press hard on the sander.. As the paper cuts the resin the dust builds up and if you press to hard the dust can't clear itself and the friction of the excess pressure heats the dust up into resin goo that in turn sticks to the paper.
It takes a while to get the right feel.. There is nothing more satisfying then reefing on the sander to get the job done fast, but without positive dust removal like a vacuum or water the disk gums up and your screwed. You will also be shocked at how fast cheap paper dulls up and in turn loads up with gop.
Google which media is better for sanding resin, it does make a differance, off the top of my head I don't remember.
Good luck and keep your respirator clean too!