issue

A strange bug:

Background:
rt-n66u+ 2020.3 (also tested in 2020.2)+ PPPoE connect to fibre modem.

Symptom:
Packet loss occasionally, MTR result showing micro-disconnection between my router <-> first ISP hop.
Drop a packet every 5~10 minutes on WAN side. (it is very concealed. Unnoticeable if I wasn't gaming or running test-tools)

My tests:
Complaint to ISP, ISP checked (they remotely test everything to the fibre modem), saying maybe something funny on my home router.
I turn on/off WAN...

issue