Thanks you for your time and your answer.
Like you suggest, I tried with a new sensor bar at a new place and with a new wiimote (that have never been saved with my system) and I got the same behaviour from the Wii U. So the problem seems to come from the Wii U itself.
Since the Gamepad worked (that use a modified Wifi protocol) and not my wiimotes, maybe I got a problem on the Wii U with the bluetooth hardware...nothing I can change about this.
If you have any others suggetions I'll be happy to here it, but I feared that I'll need to replace my system...
Thanks for your help.