Is there any way to downgrade both the App, Controller Firmware and Drone Firmware?  I am confident the last updates are causing problems with transmission power.

Same for me...

Firmware on the AC and RC can be downgraded unless it states otherwise by DJI in the release notes. I don't believe the app version can be downgraded on your device once upgraded.

I need to ask...
Why it's not possible ?
I mean,how hard it would be to have the previous Go 4 app version available?
Here is a perfect example of how useful it would be to have such a feature
For the last month i've been enjoying really good flying,not perfect but good enough.
I re-install the Go 4 app,without knowing that the app have been upgrade and my "flying experience"
take a serious hit because of that very app
In any normal "business model" you always have the option to go back few versions or at the very
least the previous one in case you having trouble with the new version,
Now you are telling me...sorry..."have fun with are new Go 4 app"...
Make the old app version available and you will have so much less complain.
We could find the right combination of firmware and app version in order to have the least amount of problem.
The way it's working right now does not encourage upgrading the app at all,unless you already have a ... load of problems and you have nothing to lose...

I firmly believe that since DJI is the leader in this segment, in conjunction with their working with the FAA, along with getting bad press from time to time, they are just going to error on the side of further compliance and rules forced upon us from the FAA and commercial interests.  I am pretty confident they are decreasing the radio signal strength if you are barely inside a 5 mile airport restricted zone in which the drone can take off and maneuver but signal strength to the controller is reduced.  During my recent travels no where close to any type of airport restricted zone, all was fine.  I do agree, with others that there should be a way to downgrade in case a turd gets out the door.  It happens.