Thanks @David-TP , I have send a mail. The issue is definitely related to the MTU, I was specifically request by my ISP to set the MTU. I am using another router to connect with PPPoE and set the...

@David-TP I am also experiencing the same issue, my ISP also requires me to set a MTU, and my connection is very unreliable if I don't set it. You mention there is a workaround to this issue - would...