Hi,
I have one Growatt SPF 5000ES with a Pylontech us3000 battery. Recently it started misbehaving like in your case. Now I'm keeping the unit in Solar Utility Battery mode. Otherwise it doesn't provide power to the output. It tries to give power regularly, however after only 1 second it gives up. It "healed" itself for several days, however this is unpredictable.
Did your unit glitch after the firmware downgrade?
Thanks!