This is not happened to me, in fact it feels like I’d never be able to get it off if I tried. Here’s a couple of suggestions to help get it stick long term:
*Use 3M’s strongest adhesive, it’s powerful stuff and an industry standard
*clean ALL wax off of the car, clay bar if if you must, it has to be a pristine surface
*remove a few inches of the tape film coating from each side of the spoiler and pull it out so that when you place the spoiler on the car, you can pull the film away.
*do the top side of the trunk first as it’s the most noticeable if it’s not sitting flush.
*Line it up, press down on the ends so the Spoiler is in the correct positioning, and press down on the spoiler while you pull the film away
*don’t do it the commonly mistaken way which is to pull all of the film off then try to place it down in one shot
*once all the films away the spoiler should be stuck in place exactly where you wanted it and pressed into place, shouldn’t be going anywhere
Good luck. Essentially do NOT do what this guy in video does which is remove al tape in advance!! Pull remove of the film off, get a tail, make sure it’s accessible to pull, press down AND pull it away it will work this way.