Problem with logging balanced (UDP) to multiple syslog servers

I've a problem with logging balanced (UDP) to multiple syslog servers.

 

Setup in a nutshell: iRule(HSL-publisher) --> LogPublisher --> LogDestination(UDP, balanced) --> Pool (Round_Robin) with multiple syslogng(UDP) server

 

All requests seems to go to only one member in the pool. (And yes, all of the members are available and enabled in the pool). When (manually disabling the node that is used to send all the log data to, another single member takes over)

 

It looks like that the distribution option "balanced" for the Log Destination doesn't work. When I select the replicated distributed option all requests are sent to all syslog servers...

 

The log destination is configured as followed: https://support.f5.com/csp/article/K17398?sr=53263970

 

The iRule I used is copied from the following example: https://devcentral.f5.com/wiki/iRules.HSL__open.ashx?lc=1

 

We run version: BIG-IP 12.1.2 Build 0.0.249 Final

 

Does anyone have any suggestions or are facing the same issues?