hey risky, i've been trying to get that bug again to make a how to solve it (might work and might not)
remove all workshop mods, uninstall spintires mod and delete the media.zip,and the other 2 zips in spintires steam folder and texture,mesh cache folder in appdata/SpintiresMudRunner now verify your files and run the game
the issue is spintires mod making your game read older map versions rather than the workshop versions (have you been updating levels recently from like older mud runner versions?? that could cause the issue) atleast it did on my game when i loaded mahoosuc (a beta version i had before smar re-released it)