Hi Marco,
thanks for the suggestion. On first test I went minimalistic on the things config as you suggested.
This actually elliminiated the received L-Data request - ignore warnings :
2021-12-29 14:58:16.772 [WARN ] [Xnet/IP Tunneling 192.168.1.222:3671] - received L-Data request - ignore 1.1.254->15.15.12 L_Data.req, system priority hop count 6 repeat, tpdu 81
2021-12-29 14:58:19.774 [WARN ] [Xnet/IP Tunneling 192.168.1.222:3671] - received L-Data request - ignore 1.1.254->15.15.12 L_Data.req, system priority hop count 6 repeat, tpdu 81
2021-12-29 14:58:22.775 [WARN ] [Xnet/IP Tunneling 192.168.1.222:3671] - received L-Data request - ignore 1.1.254->15.15.12 L_Data.req, system priority hop count 6 repeat, tpdu 81
The “no confirmation reply” and “disconnected not gracefully (timeout)” continued to appear 
I finally gave it a try to operate in router mode and this actually works without any error using the broadcast ip where my Jung router listens to.
I think this is proably more a Calimero KNX Binding thing than a OpenHAB issue. It should actually work in TUNNEL mode too to my understanding.
Meanwhile I found a similar issue: knx IP issue so I guess we are not alone with this “problem”.
Hmm as for me I can run with Router mode but all my predessesor versions 1.7, 1.8,2.5 were running in TUNNEL model. I would like to understand the root cause here.
M