Cron not working after reinstall

Debugging SickBeard is a little beyonf the remit of this forum, but I’ll make an educated guess that cron is starting it too early.

If correct, you have a couple of options:

Place your startup command in a wrapper script, that does something along the lines of:

while I can't ping google
  sleep 10
done
run Sickbeard

but that’s pretty hacky, IMO.

Since you want it to run at startup, I’d recommend you create a systemd .service file and enable it to run at startup. Here’s a thread about getting SickRage to run at startup:

since they’re related, it should be a good starting point.