UV Sanding Resin

I have been using UV cure poly laminating resin for a long time and I always used surfacing agent in the sanding coat. Often my sanding coat still remains tacky and difficult to sand. It gums up the sand paper quickly. Recently I tried just buying UV cure sanding resin, I am assuming it just has the surfacing agent in it already. However I am still having the same problem... a tacky finish.

I try to make sure that the resin is warm, sometimes I put the can in a bucket of hot water to make sure the surfacing agent is not cloudy but it doesn't seem to help.

What am I doing wrong, or are there any tips I am unaware of?

Thanks