Collision is glitchy

I am creating a flight sim.

I’ve created my mesh collider, an error bumped up saying that the vertex is over 60k.
So, I’ve decided to convex it, which works pretty well in some cases.

When my plane collide with the tag “Ground” everything works well, explosion and etc.
However, when my plane collide with the tag “Water” nothing happens, what’s making it stranger that whenever I decide to convex the water mesh, it does collide.
Any solution? is it a glitch or something?

Mesh colliders are expensive and are subject to back face culling - so you won’t get collisions in certain circumstances dependent on the camera position. The best idea is to make rough primitive colliders and attach them to your mesh, this will work a lot more quickly and will not have the back face issue.