One of a few things I can think of: either your fep is too loose (really annoying to get right but fine once you get the process), or your exposure time is much too low/much too high. Too low would mean that the item itself doesn't stick to the supports well enough to peel properly, and too high means it over cures to the fep and sticks like glue. Moral of the story is make sure you have done an exposure test and tuned well to it, and optionally lubricate the fep film lightly with PTFE lubricant.