found a new strange issue with my TV 40PFL5007K/12 FW 89

This morning I was suddenly frequently app. every 2 minutes surprised with a grey popup window to setup up the WIFI Adapter (even I have a LAN cable installed since month)
Didn't think about that rubbish and always keyed No to that mad setup demand. The request stopped asking after I think 3 or 4 times.

This afternoon I had a try with Smart TV and I saw the TV had obviously lost the LAN connection, even I have'nt done anything with it since month. Beside of rejecting the WIFI setup this morning.

So I assume the TV didn't get an IP adress whyever and asked to setup the WIFI confi again and again.

I have a AVM 7270 router and connected 3 WIFI devices, a PS3, a printer and the TV by LAN to that router.
The TV MAC address is 18:8E: D5:5C:33:41

Anyone else experianced this issue ?
What needs to be done to rule out this new to me failure ?
Why doesn't that silly device show an easy clear message when it has no IP, even some major features at the TV work with active internet connection only ?