Hi,
ok, I understand where is the problem as I am going through your thread.
if you disable the singleton GameObject, that is a problem indeed, because when you run the Fsm Again the singleton action will kick in and destroy itself because it thinks that singleton reference is already up.
the solution is very simple:
1: on your fsm with the singleton action, move to an empty state on finish.
2: uncheck that fsm "Reset on Disable"
now the fsm responsible for enforcing the singleton, only go through the state with the singletonManager once, you can disable and enable, that fsm is not going to restart.
Let me know if this is ok as a solution for you.
bye,
Jean