Should I be seeing this?
Apr 30 14:57:06 unbound[90648:3] info: generate keytag query _ta-4f66. NULL IN
This repeats for as long as it is left to run. About every 25 minutes.
I don't see anything else informative, unless I re(load|start) unbound.
Thanks! 
See RFC 8145. I think it's fair to say that this mechanism had worthy goals but unfortunately turned out to be useless.
I don't remember if there's a way to turn it off in unbound. but I think it's fine to turn off.
Joe
Should I be seeing this?
Apr 30 14:57:06 unbound[90648:3] info: generate keytag query _ta-4f66. NULL IN
This repeats for as long as it is left to run. About every 25 minutes.
I don't see anything else informative, unless I re(load|start) unbound.
See RFC 8145. I think it's fair to say that this mechanism had worthy goals but
unfortunately turned out to be useless.
Ahh. Indeed. Thanks.
I don't remember if there's a way to turn it off in unbound. but I think it's fine
to turn off.
trust-anchor-signaling: no (defaults to yes)
Joe
Thanks for the informative reply, Joe! 
--Chris