Again, there is no hard requirement that all packets in a flow take the same route. Keeping the TCP state machine POP-local when running anycast TCP is exposing a buggy TCP implementation to the Internet. I understand that it is desirable to do so, especially under calm routing conditions where it tends to work, but it is not correct.

I agree that Arista shouldn't be mangling TTL here. However, TTL mangling shouldn't break TCP because TTLs can already change under normal operation, e.g. when routes change, which happens all the time on the Internet. In a non-anycast situation, TCP connections would stay open under these conditions.