On my Enoch server managed on Nitrado I have been able to spawn Humvee's with loot, they spawn in the loot is there and the vehicle stays for its set lifetime.

I have tried to add loot to all other vehicles, I have made sure I have stayed within the slot limits and cautiously left a buffer of 30-50 slots remaining free. When the vehicles spawn in they are instantly despawning. They all have the exact same parameters as the Humvee event however The despawn within 30secs of spawning in.

I have removed all loot and the vehicles spawn in perfectly and remain for their lifetime.