You're on your own, now
Upon a reboot of my rpi2 to install milhouse nightly build of LibreELEC service.webgrabplus was restarted and back into every six hour EPG update + my cron job 03:00. (Assume because it Stops but does not fully Disable service, when disabling the WebGrab+Plus service addon?)
So for now in summary :-
1. Disabled WebGrab+Plus service via the Kodi Ui (Fully disables addon, but currently believe does not fully disable service?)
2. Disabled service via the command line (systemctl stop service.webgrabplus, then systemctl disable service.webgrabplus)
3. Utilising a cron job to run webgrabplus.start automatically and only once a day at 03:00