I tried to animate a USD automobile asset using a car rig, as seen in the video below, and then exported the animation in USD to import into Solaris and combine it with the original USD due to material concerns. However, when I combine the car parts, they go crazy. Do you know why?

so if i have to work on the asset which i imported in stage Solaris more like usd asset, what is the effective way to bring that object in to sop level do the fx stuff and bring back to stage with fx and puling material form original file.

why usd texture not showing in sop level??

I had exactly the same challenge. That‘s a case where USD sub-layering comes handy. In stage I started with the static fully textured car and sub-layered the animation from the SOP context.

I can give more details when I have access to my project.

you shouldnt need a merge node, just plug the output of sublayer 1, in to the input 1 of sublayer2.
this should just change the opinions of the geometry from the first sublayer.

the other thing you should figure out , between sublayer1 and sublayer2 the /meshes decendant count changes, which could mean the hierarchy for the two sets of meshes is different. that will make it so there is an animation mismatch for sure.

i would check that the hierarchy and names match 100% between the the lookdev setup in sublayer1 and any work your doing in the sop level car rig.