I booted my M3 with ArchLinuxArm (2018-08-22) without any problem. Then I thought it was a good idea to delete the partitions on the EMMC (that I set some months ago) to clean them up, and rebooted. Since then, nothing happens, apart from a blinking cursor at boot time.
Took the SD disk from it, and pushed in another M3 device, and it works. So my boot disk (on SD) is stil working OK. Possible that it tries to boot on the EMMC and, not finding anything there, just hangs?