Hi,
Actually the major problem was the --netfilter-mode=off parameter. Because openWRT on gl-xe300 is < 23.0.5, you want this parameter off.
You can get a more detailled explanation right here : Making sure you're not a bot!
As mentioned in another post, there is a lot of timeout and the connection remain unstable.
See : GL-XE300 Puli and Tailscale - #4 by aaloco
Thank you sir,