@td47 thanks for the answer. That happens with antenna tv, ps4, or netflix. I tried several time with all the options. At the end i decided for the drastic option, reset to factory settings.. and it worked!! Now that yellow line doesn't show up. I think that was my fault.
I figured it out. After some packet monitoring, the LG TV's reach out to 136.166.4.75. After creating a rule to deny traffic to this address from my network, the TV can no longer reach the services required to check and apply updates.