I have a laboratory set up and testing IPv6 over PPPoE.

The PPPoE server is mikrotik, the PPPoE client is mikrotik.

Problem: Some WEB pages do not open when using IPv6 (these pages have IPv6 support and open normally using TP-link routers).
I can only access these pages when I create a MANGLE on IPv6:
Mangle: TCP Syn, Change MSS, Clamp to PMTU

Detail: There is no configuration that prevents ICMP packets from going forward

MTU and MRU PPPoe Client and Server: 1492
MTU between client router and my PC: 1500


Note: I have not found a topic on the subject.

I am very grateful to those who help me.