Recently i used a extension cable to get my aeon-labs z-stick away from my core, more towards my z-wave network, so there was no interference from my core on the stick.
Before it was plugged in the back of my core. I also positioned the z-stick vertikal.
I found a article online, discribing this as the recommended way.
After some testing i found out that my z-wave network responded much better.
Even a battery operated sensor, which previously responded every now and then, now responce great.
Thanks for the suggestion, I think it's already vertically oriented however. This test node, as well as the 30 or so others that I have in my house, have been behaving beautifully over the last year in their current config / placement /etc. I don't know if it is my Zstick that is failing, or recent changes to the LMCE Zwave implementation, a prankster hacker, or something else that is to blame, but something is definitely up.
The test node survived the night this time, and has about 12 hours of uptime now. I'll keep an eye on it.