And before you ask,I have tested for myself a dozen times and tried almost every method,Here are others thing to add----
The vehicles.awc file is under 15.7mb;
"American Sirens Pack "installed;
All my XML file are from the corresponding vehicle files;
No LSPDFR or other plugins except ELS.
The only change I made is renaming a police yft/ytd into sheriff2 to better match its Tahoe model.
The method of changing numbers in Carvariantion.meta has been proved failed in my case.
I added other civilian vehicle mods and all my mods are replace mods
I didn’t even notice this problem before because I spent a lot of time making my modded GTAV stable enough.
So,for now my guess is that certain ELS vehicle(s)/corresponding els xml is/are broken and leads to complete crash for all the other sirens.But that's pretty weird because if that happened before,the comment section below respective mods would mention it,but I didn't see any