Conversion Issues with certain blocks

[ScampiTheSighted]

Greetings, I've noticed a number of blocks don't convert properly. Blocks like furnaces, pistons, and many others are simply missing in the vmf, blocks like iron bars, buttons, and slabs are whole blocks instead their correct sizes, and blocks such as chests, stairs, and vines show up as solid blocks with the 'crate' texture.

Fences, torches, and glass panes ARE the correct size and shape, though, and a flame particle generator and light source is spawned on top of each torch.

I'm using version 3.1, and minecraft version 1.15. Any ideas on what's causing this?