You might want to disclose your RC firmware version, the craft firmware version, and the GO app version. The guys here can tell you if they are compatible.
It appears to me you didn't updated your craft firmware, that's usually the first step, BEFORE updating RC firmware. If you only updated the RC and Go, that may be your problem. Then you went back to 1.6.0 firmware in the RC, which may not be compatible with the new GO app you have.
After repeated experimenting with re-upgrade and re-downgrades, my findings are as follows:
1. In late October when the video downlink problem first surfaced after I upgraded to 1.8, I downgraded my RC firmware to 1.5.80. There was no problem with video downlink problem. But I could not start my drone either when I pulled the two sticks together towards the bottom. There was simply no response.
2. After the new P4 firmware 01.02.0602 was out I upgraded it. After that I re-upgraded the RC to 1.8 again (because some people say if you upgrade the RC firmware AFTER the drone firmware upgrade, it would work). The control of the drone returned. But the video downlink corruption also returned.
3. I then downgraded the RC again to 1.6 (my drone firmware remained at 01.02.0602 throughout). The video downlink problem is solved, and the control of the drone also returned to normal, but with a reminder that on DJI Go App that I need to upgrade my firmware. I will ignore it.
With the Phantom 4 on 01.02.0602 and DJI GO app 3.0.1 (Android), my experience is that:
1. RC firmware 1.5.8. – no problem with downlink. But problem with control of the drone.
2. RC firmware 1.6 – no problem with video downlink, and no problem with control of the drone.
3. RC firmware 1.8 – problem with video downlink, and no problem with control of the drone.
The same result is found with my Samsung Note 4, and also with my Carl Zeiss Cinemizer goggles, which I use for FPV flying. So hardware is not the problem.
I think there is little doubt that the latest RC firmware 1.8 is the root cause of the video downlink problem. It has nothing to do with SD card problem (at least in my case) as the video recording is perfectly good and normal even when the video downlink is garbled.
I have written to DJI and also posted this thread to them. They told me their engineer would look into the problem. May be they would fix it with the DJI Go App 3.0.2 (Android), I don't know.