If they had been using sticky sessions, this should have been a problem before, but to a lesser extent. The same server would have needed to process all of the requests for a single client. You'd still have spikey metrics.

This might not be such a problem with one client artificially limited to a single application server. But in practice, it means that individual servers will be overloaded when they are chosen to handle multiple clients concurrently (while other servers are idle).