iRule in system log

Hello,

I installed a new BIG-IP VE 15.1.3 appliance and I see some strange behaviour in the logs.

In the system log, I have the following line that constantly appears at an interval of 20 mins :

...
Mon Jul 26 03:40:01 CEST 2021		bigip.example.com	syslog-ng	)
Mon Jul 26 04:00:01 CEST 2021		bigip.example.com	syslog-ng	)
Mon Jul 26 04:20:01 CEST 2021		bigip.example.com	syslog-ng	)
Mon Jul 26 04:40:01 CEST 2021		bigip.example.com	syslog-ng	)
Mon Jul 26 05:00:01 CEST 2021		bigip.example.com	syslog-ng	)
Mon Jul 26 05:20:01 CEST 2021		bigip.example.com	syslog-ng	)
...

And when I update an iRule, the code of the iRule appear in the System log too.

For example, if I create a new iRule with this content :

when HTTP_REQUEST { 
 if { ! ( [HTTP::header exists "X-Forwarded-Proto" ] ) } {
  HTTP::header insert "X-Forwarded-Proto" "https"
 }
}

Then I have the following that appear in the system log : 

...
Mon Jul 26 11:23:20 CEST 2021		bigip.example.com	syslog-ng		}" } } [Status=Command OK]
Mon Jul 26 11:23:20 CEST 2021		bigip.example.com	syslog-ng		}
Mon Jul 26 11:23:20 CEST 2021		bigip.example.com	HTTP			:header insert \"X-Forwarded-Proto\" \"https\"
Mon Jul 26 11:23:20 CEST 2021		bigip.example.com	if { ! ( [HTTP		:header exists \"X-Forwarded-Proto\" ] ) } {
...

Does someone have an idea why this is happening and if it is possible to avoid this ?