It crashed upon opening the terrain editor in-game 
I saw the tetris logo for like, 1 second 

So why the terrains you uploaded don't have the "SOIL" file like other WA terrain ?

Error log uploaded

TEXT.img is the thumbnail in the editor to show the texture for BIT/LEV maps.
SOIL.img is the thumbnail to show destroyed soil texture of PNG maps and reside in Data/Custom/[texture] folders.

So i'm not sure why there is a SOIL.img in *some* of the Data/Level/[texture] folders, I don't think there needs to be (I might be wrong).

If you want to use these terrains with 3.6.31.0, I think your only option is to put the level.dir in an existing texture folder... and use the FileOverride module (http://worms2d.info/WormKit)