Matt Tillman

Yeah that's odd. Looks a bit like what the resample was doing. The fractional frames had the pivots going all over the place.

Weird that it worked on my end.
Did the Cache LOP set to 0.25 work? (In the scene file I sent).

From what I can see there's not enough samples. If you turn on "Enable playback at fractional frames" you can actually see the wheels collapsing in the viewport.
The simple solution is to increase the amount of samples by lowering the increment (of the start/end/inc parameter) of the export.
Here's a reference flipbook comparing caching at 1, 0.5 and 0.25.

The "Resample Transforms" LOP I think is meant to correct issues like this without having to cache with more steps but it didn't work here for some reason (it made the wheels go haywire). I'll submit a bug report.

Some other unrelated improvements I would suggest:
- Set "Packed primitives" to "Create Xforms" so you don't end up with a bunch of unneeded prototype primitives
- Set "Topology Attributes" to "Static" (assuming there's no mesh deformation)
- Set "Set Default Values" to "* ^transform" (assuming your attributes are static)

Those options give you a cleaner tree and won't cache your attributes for every timestep. Your current setup caches not only your transforms but also the mesh, normals, uvs, etc for every single timestep, which is wasteful.
Personally, I recommend caching from LOPs rather than SOPs so that you can curate your scene graph tree and troubleshoot any USD issues before caching.

Hope that helps!

Try putting the material library down at the bottom of the LOP network. It could be that there is a lot of scene/tree reevaluation being recooked further down whenever you change things in the material.
Just a thought.