The dig output looks ok.
Your debug output is slightly different from mine when do the same.
I dont have a "rrset failed to verify" message for example.
This might indicate some faulty configuration or maybe not.
Have you enabled the DNSSEC setting in Pi-hole ?
Try disable that one and see if improves.
You dont need DNSSEC between pihole-FTL and unbound plus in the past, DNSSEC caused troubles for the embedded dnsmasq.
Else if no one else comes up with suggestions, I would try start fresh again:
EDIT:
Not the file at that particular location /var/lib/unbound/root.hints
Only the ones at:
pi@ph5:~ $ dpkg -S root.hints
dns-root-data: /usr/share/dns/root.hints
dns-root-data: /usr/share/dns/root.hints.sig
unbound should pick this one up if I remeber correctly.
EDIT2: ow and when purge unbound, take note of any messages about apt not removing particular files or folders.
Those files left behind could also cause issues.