I have a remote cron job that scrapes data using selenium every 30 minutes. Roughly 1 in 10 times the selenium script fails. When the script fails, I get an error output instead (various selenium error messages). Does this cause the cron job to stop? Shouldn't crontab try to run the script again in 30 minutes?
After a failed attempt, when I type crontab -l, it still shows my cron job. 
How do I ensure that the crontab tries again in 30 minutes?
Who is sending the error output?  If it's the cron daemon, then your job should be dead; if the selenium process itself is sending the mail, then it may still be running, and stuck.
Does cron job persist/run again if the python script fails?