question

@FanFan, I think Anthony's answer still persists. But I would also test if you can overcome this restriction by stopping all items. Then I would set negative speed in order of connected conveyors by their rank in model tree or vice versa.

Or I would try to set speed by order of connection sequence in model space. Here I would test this in opposite direction, too. Aditionally I would break up the loop to get a defined end and start of the system. This can be a queue by start as bridge in your loop.

There is also a possibility that doing this all together in a direct sequence of source code, the FlexSim engine is not able to take into account that events have happening correctly. In Process Flow you would add breath delay activities into your logic. In a source code directly, I would call my code reversely by command nodefunction and a structure build of switch by case.