I had previously assigned "discovery-beta.wmflabs.org" to an instance (on shiny-r project). I forgot to delete the proxy before deleting the instance, and now the web proxy seems to still exist but is hidden from me on Horizon. When I try to create the same proxy to point to the replacement instance, I get "Error: Duplicate RecordSet"
For the same reason I also can't create the web proxy "discovery.wmflabs.org" that point to our production-release dashboards that our product managers use, hence the Unbreak Now! priority.
P.S. Creating an instance of the same name as the deleted one caused the same roles to be applied to it. Seems like there is an issue of cached settings or stuff not being properly deleted in general.