208.201.224.11 and 208.201.224.33, carved out of one of our first IP allocations, have been Sonic’s official recursive DNS servers for as long as 20 years. Unfortunately, for various reasons, we need must deprecate this legacy IP assignment and have added 50.0.1.1 and 50.0.2.2 to our recursive DNS clusters to take their place. If you have statically configured DNS servers feel free to update them at any time. We will migrate server assigned DNS to the new IPs at our convenience. The legacy IPs will continue to work indefinitely.  – System Operations
You need to update the Sonic Quick Reference Guide https://help.sonic.com/hc/en-us/articles/235972488-Quick-Reference-Guide (point 3.1) with the new 50.0.1.1 and 50.0.2.2 addresses.
Also, in that Quick Reference Guide (point 3.1), you have a highlighted term “List of recursive DNS servers” which points to https://wiki.sonic.net/wiki/List_of_recursive_DNS_servers which is a dead link. I tried a few searches on your help and wiki sites but I couldn’t find the correct link for a list of Sonic’s recursive DNS servers. It’s possible this dead link goes back to the days when you had both non-DNSSEC and DNSSEC servers; or, it may refer to your optional Secondary DNS service; or who knows what this dead link used to be for.
Thanks for the heads up, Tom. We’ve updated the documentation on our end to reflect the changes. That link is a remnant from days of yore and the quick reference guide should now be current!
Any chance of adding DoT support to these servers?
We currently don’t have plans for that, but there is a discussion in the forums about it for more information https://forums.sonic.net/viewtopic.php?f=10&t=15026&hilit=doh.