As someone who's worked on some very similar problems, fix it properly on the vehicle side. Lamport/vector clocks are not a silver bullet here. They can be very difficult for end users to handle properly, and don't necessarily scale well in large fleets with unbounded drift. The vehicle network has a synchronized notion of time already. If the vehicles were designed properly, that's hooked into GNSS already. Even if they aren't (e.g. because it would impose unacceptably high uptime requirements), you have another system to bound drift already because various systems are required to stay within a small margin of "true" time (certificate validation comes to mind).

This is a fundamental system for the company, so it's worth cracking a few heads over the issue.