PPPOE client doesn't load some websites

Hi

I have a rb951ui-2hnd and a pppoe client on it
Everything was ok
suddenly some websites don’t load at all
I checked these:
Firewall
DNS
MTU: 1492
There are two dynamic rules at mangle : Change mss clamping …
I don’t know what should I do now!
Any idea?
Tnx

Sounds like it might be a fragmentation problem, change PPPoE MTU back to 1480, test again

1455-1480 caused a fragmenttation and under 1455 caused timed out!
20200610_171855~2.jpg

1455-1492 caused a fragmentation and under 1455 caused time out!

Why don’t you just leave the MTU settings to default, the PPPoE client will then detect correct MTU size
PPPoE MTU.JPG