If it can help developers to track this bug :

In our last (private) multiplayer race two players experience the same problem :
The cars brutally stops and the fuel was reset to our race start level. This time, I have video capture to show it.

Both issues were in the same multiplayer PS4 lobby :

Lap 8:
the gearbox switches to R, and fuel level (30.8) was reset to 48.

Lap 2 :
https://www.twitch.tv/thedaaart/v/56606512 at 00:12:29
the gearbox switches to neutral, and fuel level (about 72.x) was reset to 75

Thanks for listening.
I hope you could track it and correct it in a future patch.