Unfortunately I don’t think there is a command to do a hard power cycle kind of reboot. What I can think of is add sleep timer in the script and adjust the value until you get everything working correctly.
I too have issue that sometimes certain cronjob failed to load properly. I did it in a dumb way, make a copy of all running cronjob in /jffs/configs/cronjob.add and load it in post-mount script. The downside is if there is any addons update that changes the cronjob then I have stop this to get the updated cronjob and update my copy. It is really not a good to solve the issue. I may get rid of this soon.
Code:
# Add cronjobs to cron
/bin/sleep 5s # give the disk 5 sec to really be ready
crontab -u admin /jffs/configs/cronjobs.add
logger "Manual cronjob added"