Walk us through what you are doing step by step and do not leave anything out, including how you format the card. Again...step by step. Also indicate the make and specs of the card you are using. The more information you can include in your post, the faster you might find an answer.
The micro SD card port on the CGO4 is for some sort of service function probably software/firmware updates. I have not been able to get a straight answer from Yuneec and that knowledge is now probably lost at least here in the USA. The SD card port is part of the converted Panasonic GH4 and the location to save photos and video.
Went to Best Buy yesterday but they were all out of stock. Ordered a new SanDisc from Amazon yesterday. Will get it Monday. Will try it first with camera installed on “Proaction” unit right out of packaging. When I tried the last one in the Proaction, the app indicated the the disc had been improperly formatted. I’ll keep my fingers crossed that this is all the problem is.