When you got that new cylinder and had it filled...did the propane place 'purge' it of AIR? DId you tell them it was a NEW cylinder?
If not properly purged first filling then air is mixed with propane and can causes issues.
Propane coming from vent on regulator....regulator diaphragm is cracked. Regulator is junk.
1st reg may have not been bad....restricted flow was probably due to 'excess flow device' being tripped inside the BIG Green Nut on pigtail hose from 'cylinder' to regulator
To reset you close cylinder valve....wait 30 seconds and then SLOWLY open valve again.