I have a 64GB SanDisk Extreme PRO microSDXC Memory Card in my C5, bought directly from Sandisk on UK Amazon store here:
 https://www.amazon.co.uk/dp/B06XYT37NK/ref=pe_3187911_189395841_TE_dp_1 
 The current firmware version installed is C5.20170802.V0.22. I've been testing this before install and I get an issue whereby the device crashes, I lose WIFI connectivity, the green light stays on and the red light flashes 3 times per second. According to the instructions this indicates that the SD card has been removed but it's still in there? Is there a way to restart the device otherwise I have to wait for the battery to go flat and start all over again! This has happened 3 times now and I'm getting fed up with the device to be honest. Can anyone help? Thanks