Sometimes the game will shuffle settler assignments like every few days, I believe this is a vanilla behavior that probably can't be avoided. If you have more job plots than settlers this can potentially result in ending up with no one being assigned to the caravan which would cause the settlement to disconnect from caravan network or even multiple settlements disconnecting, if that settlement was a central one connecting multiple. This can cause a cascade effect of sorts if the settlement was relying on caravan network produced resources in order to pay plot operating costs or for scrap capacity, where disconnection can cause there to not be enough resources or too little capacity for the settlement. People on the forums had commented a lot about random or unexpected caravan network disconnections and it seems like this is probably why, alongside possible power grid issues being another potential cause. They had believed they had accounted for everything to where costs, power requirement, settler assignment should be met. People had several suggestions for SS2 changes to try to address this including an auto-assignment priority order or grace period for Caravan Services plots, but I'm not sure if either are possible to do. So I decided to try experimenting with mine with changes that I think could help with this, changes that seem like they'd be effective based on what I know and generally I don't frequently experience unexpected Caravan Network breaks.
The 2nd settler slot is there in effort to reduce the chances of no one being assigned to the caravan plot, alongside other changes intended to reduce the chances of the plot shutting down & causing unexpected disconnection from the caravan network. Another benefit is you'll be able to use a 2nd Salvage Beacon without waiting. For now, the costs/penalties do not increase on 1x1 Portable Caravan while a 2nd settler is assigned. But this can change based on feedback, if people feel it's underpowered or overpowered. Normally plot outputs are stacked for every occupant on it, double for 2, triple for 3, etc. But for Caravans there's no output that's multiplied, range doesn't change either. It also already can function the same as an IDEK Logistics if you have
IDEK Logistics Station 2 installed.
I have another Caravan Services plot idea in mind to potentially try to address this from a different angle in a somewhat different way as well.