In a non-modified openHABian setup, systemd would supervise the Java process running and restart it if needed.
But if you instruct it to stop openHAB (various syntaxes, e.g. systemctl stop service.openhab2) then it’ll not restart until you tell it to (… start …).
Possibly so. If your debug logs don’t show anything to tackle, I’d re-install the openHABian image to a new SD card. And follow the guidelines this time.