Why is epoxy clogging your sandpaper?

Usual result is it comes off as dust, not sticky... unless you try to sand too soon, in which case that residue may be somewhat toxic owing to the incomplete reaction between resin & hardener.

Best not to inhale that stuff or the sanding dust either, it doesn't play well with our human bodies' tissues.

   Green epoxy is best tooled with a cabinet or paint scraper. Try it, you will like it.

As mentioned, don't sand it.