@Berick
That's not really much.
Maybe you can find more details, when running the browser debugging mode.

I got a similar problem solved by adding this response header:

http-response header set > name: content-security-policy, fmt: upgrade-insecure-requests

You can try, but not sure if this helps.

Yeah, you're right
I followed many thread before posting here. Most of thread are dated from 2016 and some guys running my issue. They resolved it by repluging this f#!* livebox and maybe the others don't care about random disconnection.

I'm really motivate to resolve this. I attach my full dhclient log (clog /var/log/dhcpd.log | grep dhclient). As you can see, the longuest disconnection is 26 sept. I replugged my box in the evening.
dhclient.zip