Has anyone found a good way to troubleshoot and confirm these suspicions? This aligns with our experiences as well since adding more Chromecast devices and Google Home devices.
This tcpdump should show mDNS packets -- if you're getting hundreds per second (in some seconds), like I was, that's probably a good indication that something is misbehaving (or that you have a _really_ big network). If googlecast shows up in the name, it's probably Google Cast misbehaving.