I would just go back into the scene and replace the primitives that don't work and re-export. This would be much quicker than trying to troubleshoot the originals. Leave the old ones in place temporarily so you have position and scale reference when making the new ones, then delete the originals before exporting.

Yeah, I just tried replacing one the primitives, and that didn't change anything. But now I'm thinking the problem is in the animation bank, not the .msh itself. Do you know how to work with those? I am using the basepose.msh from BF1 Mod tools, and it is odd to me that it is only 5 kb big, while the basepose of the acklay is 44 kb and the basepose of a human is 104 kb. Could a basepose originally meant for a animated control building be very different than one for a playable character?

I looked further in and saw that the fambaa basepose skeleton doesn't have any effectors, could that cause a problem?

The Acklay skeleton is far more elaborate than the Fambaa skeleton. The best thing to do here if you want it to look good is to take the Fambaa skeleton and build a basic control rig and create some new animations.

Yeah, I don't know how to do any of that, though. :/

I tried this tutorial again with a simple human soldier, and no success there at adding a single terrain-collision cylinder either, link...

I don't know, i'm seeing conflicting info in this thread.
The ZETools export instructions say export cylinder primitives like p_-[types]-cylinder but ANDE replied in this thread saying it should be like p_cyl_somename. Maybe there is a problem exporting cylinder primitives.

The 2nd image in the first post shows a custom small sphere and cylinder in XSI, but in the first image only the custom sphere is displayed when using the debug exe, the heights of the custom cylinder and one shown ingame do not match up. I assume the first image is meant to show the result of the 2nd image. And I still have no idea where he got those step 3 instructions from.

If no one can successfully do anything with the info in this thread then i'll remove it from the FAQ, otherwise the information desperately needs an overhaul. The shipped docs already explain collision primitives well enough to understand, step 5 and 7 is really the only additional info in this thread.

I'm not aware of a problem with exporting cylinder primitives, it should work.
The code checks for "cyl" so both "cylinder" and just "cyl" will work, although "cylinder" would be the preferred naming convention.

To make sure the collision primitive export works you could try to import your exported .msh again with ZETools and see if the primitives retain their type (cube/cylinder/sphere) and properties.

So I've tried both using "cyl" and "cylinder", haven't had any success. I also did import my exported .msh and confirmed that the primitives were still the same. Could someone else try adding the primitive to this msh? I just want 1 cylinder, 2 units tall, 0.5 unit radius, and translated vertically by 1 unit, that has only terrain collision.

The acklay uses a large sphere for terrain, building and vehicle collision. Try using a sphere primitive, or multiple for precise collision and see what happens.

Just tried with a large sphere, no luck there either :/

Ultimately, I decided to keep my spectate soldier completely collisionless, and I think now I'm planning to convert an ATTE into the tankbug instead of a fambaa, so I guess I won't need to get collision primitives working. But still, it would be nice to know what I was doing wrong.