It looks like the issue is with the Source object (just named Source). It is using an Arrival Schedule for the Arrival Style, and the Repeat Table option is checked. However, the table only has one arrival, which is creating an infinite loop. So in this case, Source is essentially creating "infinite" items in 0 time, and that is holding up the rest of the model.
Please note, that just changing the ArrivalTime to something greater than 0 doesn't fix the issue, because the problem is having one arrival (or all arrivals using the same ArrivalTime) and then using the Repeat Table option.
The solution is to either clear the Repeat Table option so the schedule isn't repeating, or to add another arrival in the Arrival Schedule table with a time greater than 0 (or greater than the first arrival's time). Or, if you just want Source to continuously create items as often as possible, you can change the Arrival Style to Inter-Arrival Time and set the Inter-Arrival Time to 0.
