My system disk is a 120 GB SSD - i have one of those sata to usb cables that has usb 2.0 (power) and usb 3.0 (data) connectors so I guess the SSD has enough power.
I tried and learned that the reason is probably the SD card itself. I tried with two SD cards. First is Sandisk Ultra 32 GB and second is Verbatim 8 GB class10. The process of preparing was the same - I've burned the last stretch image with etcher. SanDisk reboots and Verbatim doesen't. So I guess the main reason is the speed of the card (or maybe someting else)? It seems it is important even if the system is on fast SSD. If you have any additional comments I'll be glad to hear them. Thanks!