I've been trying to import JMS files like the warthog into blender via plugins like Halo Asset Blender Development Toolset and Blendkrieg, but I notice that they don't import and export properly.

for example, when I use Halo Asset Blender Development Toolset it merges all the regions into one when exporting (but can't import properly) and Blendkrieg displaces some of the markers when importing (but can't export at all).

what should I do?

Use 3dsmax instead of that piece of garbage

Besides, the people who promote it and develop tools for it still haven't learned that the best way to keep information available and free, especially on how to solve issues, is to have a forum and not twenty different discord servers that will eventually die out without getting archived.

This is, of course, if what you're modding is Halo CE and not H3 (Dennis make a new subforum already pls)

I'm modding Halo CE

You can find active help over at the Halo Archive or the Halo Modding Reclaimers discord channels. The Blender toolset is the tool you want to use though for that, as blendkrieg is pretty old and not actively maintained.

If you want some written guidance, check out C20:
https://c20.reclaimers.net/

You can join reclaimers here:
https://discord.reclaimers.net/

Alternatively you can join Halo Archive here:
https://discord.gg/C58AqZWMK5