Looks like it is still possible to have a customer get stuck after leaving the shop... Not sure what he's stuck on, but he's forgotten to get the hell out....
He's in the middle of the road between shop and exit - and as long as he's there, no more customers.
Should probably attach 3 additional timers to them.
"spawn"
"Timer 1 - Reach the shop" a short timer that prevents them from not reaching the shop
"Time 2 - initiate at shop" (standard/already present)
"Timer 3 - Started when spawned" - A backup timer that looks to ensure they start timer 2 - If timer two doesn't initiate, timer three will remain running, and eventually despawn them
"Timer 4 - Insurance" - A backup for all of them. a long timer that cannot be overruled except by a new customer being spawned - This timer will be excessively long compared to the others to ensure they get the hell off the map. Long enough for the slowest possible walk into the shop, the entirety of the longest customer order-timer, and a bit of change for slow exit of shop, So that maybe a minute or two more than /all of that/ it despawns them