Presuming that you've mixed the resin to the correct ratio, mixed the two parts together sufficiently, and allowed the correct amount of time for them to set, it's possible that your resin is too cold. This can slow down the curing process, causing it to be sticky long after it should have fully cured.
If this is the case, place them somewhere warm and allow them additional time to cure. Overnight next to a radiator, for example. But not too close in case they warp.
If this isn't the case, you should look at any additives that you are using to color the resin.
For example, if you are using alcohol based inks that aren't properly mixed in with the resin, are allowed to sit on the surface of the resin, or if you use too much alcohol based ink and have changed the composition of the resin.
As you're experiencing the same problem with both UV and two part epoxy resin I would suggest the latter of these two may be the case.