The mod causes the textures of TNT and furnace minecarts to break - they only hold black cubes.

This is probably MC-6932 which is fixed in 1.15+. I have written this one-liner for 1.12 which seems to fix the issue, however I need to do more testing to ensure it doesn't break anything else.

I think this is just 1.12 rendering jankess that I have no control over, sadly.

Closing bc 1.12 rendering nonsense that to my knowledge can't be fixed easily

I also encountered this - my workaround was to disable them from generating in the first place through the config file.