I guess if you're migrating from VPC peering to Transit Gateways you have to coordinate updating the routing tables in both VPCs at the same time (I'm guessing

I guess if you're migrating from VPC peering to Transit Gateways you have to coordinate updating the routing tables in both VPCs at the same time (I'm guessing they probably updated routing tables in one VPC but hadn't updated them in the other yet) unless you adjust MTUs ahead of time. Seems to be a crappy migration path (execute these updates quickly and hopefully you don't drop too many packets before they apply)