Thanks @davehart. Someone else sent a similar email to the ticket system today. I haven’t had time to look in the logs (and might not for some days). I’m guessing something happened so the checks weren’t running at the normal interval and the system was left with a single server in the “servers worth considering” time window (20 minutes I believe).
I’ll confirm and figure out what the fix will be.
I’ve also been seeing scores all over the place from the new monitoring system for a couple weeks - was getting barraged with emails when you first launched back in march, has been stable for months and now I’m getting a few emails a day again with really wacky measurements pool.ntp.org: Statistics for 96.245.170.99