The DR650GW-2CH like the DR600GW and the Blackvue DR750LW-2CH cannot recognise exFAT format SDXC cards, in order to get the Blackvue DR650GW-2CH to boot up successfully with a 64GB Micro SDXC card inserted you need to format card to FAT32.
To fix this problem, use the BlackVue viewer app and the format function within it.
