Starting a few months ago, I re-caulked my shower. Everything was great until about two weeks later, when the caulk seemed to separate from the wall. I figured the caulk was bad, so I switched brands and did it all over again. Another 6 weeks in, and the caulk is not adhering. Did it again, and this time it didn’t even take two weeks. WTF is going on? I made sure that the surface was pristine before I applied the caulk. Couple of notes: the shower is one of those bath fitter things the old owners put on; feels like plastic. The tub is a regular steel tub. Also, the vertical beads seem fine; its just the part where the caulk meets the shower surround that isn’t adhering (its bonded fine to.the tub). Any thoughts/advice?