o Destination Unreachable (Type 1) - All codes
o Packet Too Big (Type 2)
o Time Exceeded (Type 3) - Code 0 only
o Parameter Problem (Type 4) - Codes 1 and 2 only
In particular, if it is dropping Packet Too Big packets, then you are guaranteed to have packet size problems as MTU Path Discovery will not work, and IPv6 will never fragment packets when they are too big, they will just be dropped.
Lorenceo: If MSS clamping solves the issue why not leave it on?
sorceror: ^ try dropping the segment size even lower, i'd start at 1420-1430 then tweak