Hey folks,
I want to give an update about my current hue/bj situation.
It works perfectly so far after updating my switches to the current fw status.
I traced down an additional problem with my wireless door bell… Additional to the BJ switch FW problems, my osram lightify bulbs turned on and off and on and off every few hours for no reason (yes, one of them is in our sleeping room, so this was great for the WAF). All original hue devices works perfectly in this time. The wireless door bell also had some issues (it rangs for no reason (day & night))… After removing the door bell from my setup (including wireless repeater) an migrating to anaother manufacturer everything is perfect.
So, in conclusion, I`d updated the firmware (some problems with the switch remains every few weeks). Then I searched for other wireless devices and removed them step by step. So I traced it down to the wireless door bell. Since then (3 months), my setup works like a charm.
Btw:
It`s strange to write in english with only german thread partners (when I look at the names) 
Thanks for your help,
Lars