question

https://docs.flexsim.com/en/21.2/Reference/CodingInFlexSim/FlexScriptAPIReference/Conveyor/#Property-targetSpeed

"[Reversing conveyor direction] was designed with a very specific scenario in mind, which is to give modelers the ability to simulate accumulation buffers, where items can be pulled off a main conveyor line when the line gets backed up, and then moved back onto the line when it clears out. The functionality has been tested only for this scenario. Using reversible conveyors for other scenarios has not been tested and thus may not work perfectly.

...

"No updates are made to the internal routing table when a conveyor's direction is reversed. This means, for routing purposes, i.e. when sending an item to a destination point in the system, the conveyor is always assumed to be conveying in its original direction."

Reversing conveyors was not designed for the scenario you are using. However, I was able to jury rig it to work for a single item, although there's no guarantee it will work as you scale up.

lifer-level-v3.fsm

The big thing you need to do is make sure that the conveyors' primary direction leads out of the loop. This will configure the routing table so that you can send it from somewhere in the loop to that exiting conveyor, and it will know where to go. Then, you reverse the conveyor's direction at the beginning of the simulation, so that items can get onto the loop.

The tricky thing is that you need to make sure the conveyor direction is correct at the proper times in the model: reversed when items are flowing onto loop, and normal when you are getting items off of the loop.