thunderbolt display ethernet not working

Dears,

Since a few weeks, I can't use the ethernet connection of my two thunderbolt displays from my MacBook Pro running OSX Yosemite 10.10.2.

I don't think it's a hardware problem as screens haven't been moved, network cables have not been snatch aggressively or anything of that kind.

Anyone an idea on how I can investigate that problem ?

Thanks in advance,

Lionel

P.S.: note that my thunderbolt displays are not geographically located at the same place, I have one at home and one at office