Aside from asking if the surface has been cleaned, prepared and dried properly, the next suspect is thinner. Using the wrong thinner will lead to all sorts of problems. I don't know about that particular product, but you should use whatever is recommended for thinning on the can. Another suspect, perhaps, is gelling in the pot. Epoxy can gel very fast if mixed in a container that leaves the liquid epoxy with a low surface area to volume ratio. I would use a slow hardener rather then a fast to help prevent gelling. A trick, based on the fact epoxy reaction ceases at low temperature, is to use two disposable painters cups. 1/4 fill the first with ice, then place the cup containing the epoxy paint
on top / inside of that. The low temperature reduces (even stops) the reaction of the epoxy, giving it a much longer pot life. Keeping the cans in the fridge before use also helps, and putting unused paint
in the freezer
can keep it good for the next coat as well. Good luck!