I run repetitive server with a 3D printer and a laser cnc on the same machine (raspberry pi 3). I get similar symptoms if I try to run both off USB power. Crash reboot, crash reboot. One or the other is fine, just not both. I removed one of the diodes on the 3D printer to prevent it from powering from USB. Looked like it was pulling too much power on my setup. After diode removal I can run both all the time.