I went through the FC30 stage, and ultimately moved on to Xbox One bluetooth controllers due to them being a little easier on my carpal tunnel. I had horrible problems with bluetooth disconnects on both, until I purchased/installed a USB Bluetooth adapter. Now, I have no problems at all. You'd be surprised how much this helps.
Might want to check out my advice here: https://retropie.org.uk/forum/topic/19950/xbox-one-blue-tooth-joy-pad-connection-problem/3
I believe you should only need to follow items 4 and 5 as the other instructions are Xbox One bluetooth specific. (Basically - Buy/install the adapter, disable onboard bluetooth, re-pair your joysticks/edit any additional configs items)