I've been scanning about 300+ badlands/badlands plateu chunks [MESA] and 100+ chunks of mountain [EXTREME_HILLS], where acording to the code, have a weight of 4 and I can't find a single bauxite vein. For comparison, I've found several iridium veins, which have a weight of 1, in the mountain chunks and over a dozen iridium veins in the badlands.

Oh wow, for some reason I did https://github.com/GabrielOlvH/Industrial-Revolution/blob/master/src/main/resources/data/indrev/veintypes/bauxite.json#L13. Which just fails to register this specific vein. Sorry about that and the delay for the response, I just randomly checked the debug log and found Not loading optional vein type indrev:bauxite because techreborn:iron_ore is missing lol. I'll fix that for the next update (which might take a while)
Anyways, thanks for the report!