Lifting is caused by solvents getting UNDER the substrate. That spoiler must have a poor quality primer on it already. It was either poorly prepped so the primer is just "laying on top" of the spoiler so when you apply more primer over it the solvents from the new primer get under that primer because it isn't sticking well to the spoiler, and it lifts it up.
Or, the primer that is on the spoiler is 1k or poor quality 2k and when you spray your primer over it the solvents go INTO the poor quality primer because it is "soluble", lifting it.
You can strip it all off, you can spray your primer dryer so it's solvents flash off before they can be soaked up.
Sand with a finer paper feathering out these problem areas is also often a fix. If the feathering is done with a finer paper there aren't scratches that allow the solvent to get thru.