I happened to have to same issues on all my ESXi hosts roughly one month after Upgrading from ESXi 5.5 to ESXi 6.5.
I upgraded using Updating Manager and went from a Lenovo ESXi image for my IBM servers to a VMware generic ESXi image.
/var/log/syslog.log revealed a vendor script repeatedly running and failing.
Revoking the script from scheduled tasks (cron) fixed the issue.
You may want to have a look at your cron jobs with vi:
$ vi vi /var/spool/cron/crontabs/root
