cron stops running when processing multiple items

Question

Cron stops running (no visible error) after a few hours when I add more than 5 jobs in my cron tab.

Each job runs every minute. I tried putting all of my php jobs in a shell script and called this shell script instead but the same problem occurs. Cron stops running, no error in the log file, no error email sent out either.

The PHP script uses curl to read a webpage, parses values from this web page and then inserts them into a mySQL database.

Anyone encountered this problem before? Where/how canI debug this?