Both propane cylinders valves OPEN...swapping 'in service' lever from tank to tank and RED/GREEN stays RED??
Remove pigtails from cylinders........When you turn ACME NUT (Green nut) do you get a 'piff' of propane being released?
Inside that ACME Nut is a stub that pushes open a spring loaded shut-off valve inside the valve connection. If ACME NUT not fully tightened....no flow out of cylinder
Crack outlet fitting on regulator to main hose...any 'piff' of propane
Bad regulator.
Also........check that ALL propane appliances are turned OFF when trying to reset ACME excess flow device. Valve out cylinder/wait then slowly valve back in.
Should hear click.
Anything OPEN will act like excess flow because line pressure can not build up/equalize in hoses.