I shared a large scale mission and some of the members sent ambulances and were afk for a day and my EMS wasn't able to force their transports and it ended up to where they never logged in in time to transport and everyone lost out on the payout because of not being completed. I take it your own EMS is not able to force other members to transport?
If it is a mission you shared and someone has been offline for more than 30 minutes, you can cancel their transports.
You have to click on each unit's name individually and then select the cancel transport option.
Going back to talking about auto-transport; I'm not a fan of this other than how it is currently implemented (through EMS chiefs) as it makes sense to prevent overloading of hospitals (particularly when it comes to those who only put realistic expansions at each hospital).