I can also confirm this is an issue. I've analyzed the console logs and apparently when the AI cops try to pit the suspect, an event called
Events_PedPittedAndCrashedByCop
is invoked. This makes sense that the AI cops are able to PIT but not the players because whenever the AI cops PIT, this event is getting called, allowing the actual PIT to happen. For players though, since they don't get to invoke this event, the PIT becomes almost impossible. I remember back in the 0.2 or 0.3 days we were able to PIT much easier. People may argue this adds realism due to an increased difficulty, but I'd say the LSPDFR devs should just let the players choose to have this option enabled or not.