Run the reset ipv6 pathmtu [ vpn-instancevpn-instance-name ] dynamic command in the user view to clear the PMTU entries in the buffer.
To clear statistics about packets that have been discarded because the packets' destination MAC addresses are different from an interface's MAC address or the packets' sizes exceed the interface's MTU, run the reset forward-statistics packet discard [ mac | mtu ] ipv6 { interface [ interface-typeinterface-number ] | slotslot-id } command.