Using Fabric for 1.15 and projectLUMA shaders, some odd things happen if you attempt to build a nether portal underwater, which I acknowledge is a pretty niche problem. Being underwater with the shaders on, you can't see the nether through the portal.

Which itself is not a terrible problem, but then being underwater and looking at any part not under the water/where you can see through causes everything else to turn pink.

Maybe it's fixed in 0.26