Sounds just like the problems i was having..
flown my mavic pro for over 12 months with a S7 edge & not once had this "Remote Controller connection error" or any problems at all.
Then in December i decided to treat myself to the s9+ and every flight since then i have had the same issue "Remote Controller connection error" and lose all control of the drone, lucky each and every time its returned to home. ive tried everything possible even as some suggest to buy a short usb to c cable as that was suppose to stop this happening but it was still the same for me..
anyhow ive since swapped back over to my old s7 edge just to try that & in over 10 plus flights since its never disconnected yet,.
So i now just use the old phone for the drone only & use my s9+ as a hot spot internet connection to the s7 edge.. no problems as yet..
Interesting. I have 3 1/2 hours on my Mavic 2 Zoom, and i have also an Mavic Air with 1 1/2 hours and a Spark with 4 Hours, so far no problems, except one episode with my Spark loosing connection, but that was back in February.
I have been using my LG G7 for flying, and it got updated to Android 9 on June 11, that day i flew my Mavic Air without any issue, but since then i have not been using any of my drones, except last week when i flew my Mavic 2 Zoom, and this Remote Controller Connection Error came up, and Disconnected so the GO4 goes gray.