White plane issue with certain assets from Quenching

[pepto_bimbo]

Hey everyone! I installed Quenching a couple of days ago, and have run into an issue with a bunch of the doodad assets (rocks, crates, a lot of other miscellaneous things) now have this white plane on the bottom. I don't mind trying to fix the issue myself, but I'm a complete amateur at modeling. Is there a modeling tool folks use these days that's commonly recommended, and would I be able to clean up the issue from there?

Example of the bug:

Many thanks in advance for any help people can provide.