I have SanDisk Extreme 128GB Micro SD V30 microSDXC Memory Card - SDSQXA1-128G-GN6MA in my Mini and I get SD card malfunction error most times when I try to save video to it or video recording will stop after a few seconds or almost instantly after starting. I have reformated the card in windows and through the Fly More app with no change.

Hello there jlk1969. I am sorry for the trouble this has caused and thank you for reaching out. If possible kindly please try using a different recommended SD card to isolate the issue. For reference, I will be posting  the list of recommended microSD card for the DJI Mavic Mini. Please keep us posted for further assistance. Thank you. and thank you for reaching out.

Have you tried using the SD card in another device to test it.  There are a lot of "fake" SanDisk cards for sale on the internet.  You could also try a different SD card if you have one lying around that is on the compatibility list.  Hope you get it sorted out soon.

I got one of these yesterday and works fine
SanDisk - Extreme PLUS 256GB microSDXC UHS-I Memory Card SanDisk - Extreme PLUS 256GB microSDXC UHS-I Memory Card30