How to trace cron actions?

Send the cron.* syslog facility to its own file, see How to check cron logs in Ubuntu. Review syslog crontab lines for edits, and the CRON lines for jobs run.

Review the crontab spool for users, the system wide crontab, and the .d directory.

/var/spool/cron
/etc/crontab
/etc/cron.d

The rest of the cron directories contain just scripts to run on the specified interval. These won't contain something run every minute.

/etc/cron.hourly
/etc/cron.monthly
/etc/cron.weekly
/etc/cron.daily

Linux allow administrator to check all cron jobs running on the server, since you are running Ubuntu you need to go to /var/spool/cron/crontabs then grep all configured cron to see what job is running every minute grep -r "*/1" *.

Also you need to check if there is a user running a cron job that contains a repetitive condition.