Also is are there any reports in /var/log that might give some clues?

How much RAM are you allocating to the server?

I just said that we had more mods in .18 and it worked fine.  We are using the vanilla 70 limit in both cases.  

Additional info: If one person is driving, the cones and blackwall are fairly uncommon but as soon as two or more start driving (near or far) the issue becomes as Beornvig describes. Also, speed does not seem to matter as each player could be going 30 or 100 but the issue manifests regardless.

We have also been experiencing this on our hosted server with far fewer mods than we were using in 42.17 (25 currently as opposed to 127 during the golden age of updated mods somewhere around 42.12/42.13). I think the issue is that something changed with 42.19 that was not occurring in earlier builds (at least for us) that the devs may need to know about. Mods are a supported feature of this game as is the option to change the speed limit, so if a core feature, such as driving around the map, becomes unplayable from using either of these other features perhaps it is a bug and needs to be reported?