"Unknown" syslog message

Hi everyone,

I am the happy owner of six Dell R630 with the free ESXi 6 stantard image (VMware ESXi 6.0.0 build-3620759) installed on SD cards.

The ESXis are split in two different datacenter. There is no shared storage and no vCenter. There are 4 to 12 VMs and plenty of spare resources on each host.

Sometimes, apparently at random, I experience what I can only call an "Unknown:" syslog messages storm from a host or another. Like... millions of them in a few minutes.

The log messages are just rows of :

2017-01-15T20:48:58Z Unknown:

2017-01-15T20:48:58Z Unknown:

2017-01-15T20:48:58Z Unknown:

2017-01-15T20:48:58Z Unknown:

2017-01-15T20:48:58Z Unknown:

2017-01-15T20:48:58Z Unknown:

Enough to blow the 7 logrotate history in less than a minute:

-rw-------    1 root     root          2628 Jan 15 20:48 syslog.0.gz

-rw-------    1 root     root          2629 Jan 15 20:48 syslog.1.gz

-rw-------    1 root     root          2627 Jan 15 20:48 syslog.2.gz

-rw-------    1 root     root          2626 Jan 15 20:48 syslog.3.gz

-rw-------    1 root     root          2630 Jan 15 20:48 syslog.4.gz

-rw-------    1 root     root          2628 Jan 15 20:48 syslog.5.gz

-rw-------    1 root     root          2630 Jan 15 20:48 syslog.6.gz

-rw-------    1 root     root          2630 Jan 15 20:48 syslog.7.gz

-rw-------    1 root     root        420397 Jan 15 21:08 syslog.log

And fill up our 60Go remote syslog server in a few hours (~5 hours, and more or less 405000000 rows, for only one server storming).

Killing the vmsyslogd processes is enough to stop the storm. They are automatically restarted, and i receive normal syslog messages afterward...until the next storm...

I'll dig again in the remote syslog history tomorrow. With a little luck there will be something useful but so far, nothing...

If anyone knows something about my problem or have any clue...help appreciated.

Thanks in advance.