I feel your pain Andrew as I was right where you were with Go4 about a Week ago, having previously flown ~115 rock solid flights with Go3 never faltering on my s7Edge. Go4 was crashing on me, greying out and losing connection mid flight. All the while Go3 was sweet. So I gave up on Go4 in disgust too and fully uninstalled it, until the new firmware came along. The I re installed it, updated the firmware and all has been tickety boo with it since.
So only real difference I see is I did a clean install of it with the new firmware. Might be worth a try for you too seeing it is currently unusable for you.
Uninstall it like you do any other Android app. But then take the extra step to remove all its files which will remain and will probably bork it up again when you re install. Either do this with the built in S7 file manager or by connecting to a PC.
My Files > Device Storage > Dji, then More > Edit, check the box beside dji.go.v4 and press delete.
Do same for the second dji.go.v4 folder in the root.
My Files > Device Storage then More > Edit, check the box beside dji.go.v4 and press delete.
Of course dont delete the Dji folder just the dji.go.v4 folder as it also contains your Go3 config.
Having done this, re install go 4 from the play store and finger crossed.....