BattleEyePolice

Thanks for sharing the solution!

You would be surprised at how trainers can mess up the AI, it is common enough

SOLUTION UPDATE:

Turns out that the "fix wheel turn back" (the feature where you can keep your wheels turned/locked after leaving a vehicle) or whatever it's called in the QUANTV Trainer menu had seemingly been the culprit of this issue, though I still have no idea how such a simple feature can mess the AI this much. Anyways, the moment I turned this feature off and restarted the game, I've conducted multiple traffic stops, drove around the entire map, and the issue hasn't happened since. That's probably also why it had been so inconsistent, because I actually left the wheels of my car turned only during SOME traffic stops. And after the first one, where this feature was engaged, the game just broke. It's weird, but it is what it is.

I have in fact tried reinstalling LSPDFR, the issue persists, though it's very inconsistent. After I've just launched the game and gone on duty the vehicles actually stopped/slowed down for me. Then after a couple of minutes/some distance travelled they've all gone nuts again. And it's not like they crash and stop, they quite literally keep pushing me in front of them as they become spooked/angry. It's funny, yet so frustrating as the game is unplayable like this. P.S. This is happening in story mode as well now...

I will try to record a clip when I've got some time on my hands sometime tomorrow.