Well… it looks like I owe the Local team an apology. I was troubleshooting very slow downloads from one of my servers with the folks at Vultr and in running some tests, we noticed that the connection at my end with Comcast was showing very high and very variable ping times, up to 500ms.
I restarted the cable modem and router which fixed that issue… and seems to have fixed this one. I’ll test more, but for the Local people you might want to keep this around as a known issue that affects Local, but isn’t Local’s problem per se.
To figure this out, I used mtr, a tool that exists on all platforms. See this link for details: https://www.vultr.com/docs/how-to-send-an-mtr-report-to-support