That happens if the skin pack is made wrong. Don't do an update on an updated version. This means mostly don't update the uneven version numbers. Unfortunately people still suggest to do so.
There is a character limit for skin file names. I'm not 100% sure how many characters are allowed. But it's something about 13. So BMW_M4_GT3_TEST are 15. Try to reduce the characters of the file name for the dds.
I'm no expert in this case but as far as I understood they licensed the ISI Motor Engine from ISI. Which for my understanding ist the version 2.0 which was used for rF1 and so on. ISI Motor Engine 2.5 is the one which is used by rF2 and which is the one which belongs to MSG and can't be licensed...
I have never used the "Base Material" Node. So maybe there are some options to adjust the output to get a Normal map or to identify what parts should be used for which for the metal roughnes.
I use the bake function of Substance to get a normal map. The same goes for the roughness and metal...
I'm not sure if this is the problem but could it be that you missed to pack the xSector2.gmt to the mas files?
I found this entry in your logs
55.45s steward.cpp 9043: No sector 2 poly found
Another error could be the AIW file
53.81s JNITrackInfo 104: getCurrentWaypointsForTrackSelect...
Have you checked this one? https://docs.studio-397.com/developers-guide/general-reference/dds-export-file-formats
Maybe the Nvidia plugin doesn't export as sRGB
Besides this the intel plugin works faster for me but I haven't checked the Nvidia thing for a while
I found 2 signs with the wrong visgroups assigned.
The first one is at Schwedenkreuz the km 5 sign on the right side which is visible at daylight but not at night.
Day:
Night:
The second one is before Bergwerk. The triangular shaped ! red sign on the right
Day:
Night: