Thanks for the reply George.
This issue has resolve by it self (pun intended) without me having changed anything on my end. It was an upstream issue.
Some interesting information I’ll share for posterity:
Cloudflare would also not resolve the domain in question (twitterdatadash.com). Even on my cellular device which is on a completely separate network as the unbound instance (although it would resolve using my providers default DNS).
I sent Cloudflare a DM on twitter about the issue including /cdn-cgi/trace information and the message appeared to have been read.
A few days later I checked the resolution of the domain using Cloudflare DNS and it succeeded.
I then reconfigured my unbound instance to work recursively and the domain correctly resolves.
My root.hints file remained unchanged since 12th May.
Thanks All,
BangDroid