Vanillarare

Correct!! It may ask you to replace files when you drag and drop into your Main Directory make sure you click "replace the files in the destination"

if you are talking about your police vehicles you have to remove the police vehicles from the nve vehicles
because they are clashing with eachother i had the same problem but I knew that that had to be it the taxi also does that if you replaced it the bus also does if you replaced that 
 
 
whatever patchday you use for your vehicles js look them up in the NVE Vehicles and if it pops up in nve vehicles then delete them 
remove sheriff and sheriff 2 from nve vehicles
im going to make a yt video for that 

remove all the police vehicles from nve in "NVE Vehicles.rpf and i use patch day 28 to install my police vehicles