To recreate

1. Open Minecraft
2. Make a new world
3. Place Vehicle While In Creative (same problem with every vehicle)
   
4. Change gamemode to survival
5. Left click on vehicle (to break it), You'll find missing textures. (Purple and Black)
   
6. Attempt to pick up vehicle
7. Then your game will close, with this crash report.
   crash-2021-12-20_18.07.45-server.txt

Here are the flan mods that are installed (all on beta 9)
Modern warefare content pack
Utility content pack
Titan Content Pack
Mecha Parts
WW2 content pack
Simple parts
Flans mod itself
Side Note: crafting table is also missing textures.

Oh yeah one last thing, this in a modpack I've been making for a while now. I've made sure that there are no mod conflicts as well.

Update: removed all other mods to be sure, here is a cleaner crash report. I'm wondering if I'm missing a dependency or something like that.
crash-2021-12-20_18.23.45-server.txt
(also tried using beta 10 as well)

Saw the flan folder, feel like an idiot lmao. If you were in the same spot just put your content packs in the flan folder.