The location of the env_cubemap is where the reflection snapshots are taken from, thus it is usually recommended to place them at camera level so reflections are at least height-wise correct to the player, even if the x/y isn't.
Why this case has what appear to be legitimate texture warping, I don't know. All I could suggest is fiddling with stuff, maybe assign the cubemap to the faces manually, or move it a few units, or remake it. None of which I really think should do anything, but when you don't know the cause there aren't many options.
Although, looking at it closer, I think I see some reflection seams in the floor faces. I would try manually assigning the cubemap to all the faces that make up the floor and see if that fixes it. Maybe there is some kind of cubemap blending I'm unaware of.