It was my mod, but not that one.either it's your mod or it's an issue that they managed to re-introduce.
I found that I had forgotten I was using "Next-Gen Crowd Distance LOD and Density 2024 (UPDATED)", which was actually not "UPDATED" for 2.2. This one was suspicious, so I removed it. More importantly I think was that I updated "Realistic Traffic Density" where I was using a version from April 2023.
The problem with vehicles freezing in place and disappearing behind me is gone now, I spent half an hour driving around. The traffic NPCs are actually quite good at avoiding collisions.