Pretty sure that's linked to the same bug that's been causing tires on some of the open wheel cars to dissapear after a certain distance.
Try going to assettocorsa > extension > config > graphics_adjustments config.
Create a backup of the graphic_adjustments file.
then open it and change "[VISIBLE_CARS]" values to
MAIN=2, 20, 16, 28
GBUFFER=2, 6, 12, 12
SHADOWS=2, 4, 4, 12
hopefully that helps. Might cost some FPS, I'm not 100% sure. Depends on your graphics card I guess. The more ideal situation would be for people to make mods for the most stable version of CSP rather than being forced by everyone to use these buggy and untested betas constantly.
Thanks! Unfortunately it didn't work. I set it as you described but it's still the same thing. I reported it on RD and on CSP Discord server, we'll see how it goes.