ST hub v2.0 UK Z-wave problems

Hi all,

I have two Z-wave sirens in my setup. One indoor and one outdoor.

I am having trouble with both. Sometimes i cannot reach them at all. I open up the device and send a test command and nothing happens. In the log, I can see that the command fired, but nothing happens. This has happened when (test) alarms occur as well.

I am absolutely convinced that it has to do with the Z-wave connection between the hub and the sirens.

How can i troubleshoot? Any ideas?

Thanks a lot