I do have DNSSEC validation enabled, however all tests validate successfully.
When I run
$ delv twitterdatadash.com
;; resolution failed: SERVFAIL
Use unbound-host -rvdD twitterdatadash.com
Add more -d to increase verbosity. It might reveal why its validation is failing. SERVFAIL usually means validation failure. Or network outage. Check whether its servers are not in unbound-control dump_infra.