Usually, what breaks a shield is an attack that does not correspond with the shield. For example, a devilite hit on a barbarous thorn shield. A polyp spike on owlite.

That is why most people craft one shield for each type. This leaves status resistance for desired uv's. Shock, fire, and freeze are considered to be the more dangerous status. Vps has fire, shock is rare in fsc, and freeze does not exist. So your vps doesn't really need any status uv.

The only thing that should be breaking the vps in fsc is chain rushed by a trojan, then surrounded by slags. Its made to be a real sturdy shield. If you find that shadow hits are breaking it too often, chances are you should dodge more, or use a shadow shield.

Here's another catch. While wise owlite and 4* skelly are useful for fsc, a 4* plate shield is only normal defence. Boosted plate shield, if I recall correctly. So it has no fire resist. Just a vanilla normal defence + health shield. Won't be taking much hits from anything. Spending money on uv to cover its 4* phase is a waste of resources. And unless you get lucky or spend a lot of money for a max uv, you are better off learning to play with a weaker shield than to rely on uv's.