We have verifiable metrics that the DB upgrade has worked well. We are still gathering data on the performance of the new solarsystem simulation hardware, it has only been a month and half in the cluster; but so far, so good.
Re. the issues you describe: Chat is not hosted in the London datacenter at all; rather it is in AWS Ireland and the EVE Client connects directly to it. Same goes for Search, and then Contracts rely on Search to look up types and characters. So these hardware upgrades would not have affected that one way or another. We are aware of some gnarly and difficult-to-repro issues with Search after we updated to the latest version of AWS’ OpenSearch but they are being looked at.