Is your ISP Virgin Media and are you using their Hub 5 router?
That router breaks DNSSEC TCP replies. It also fails to resolve .tv domains.
The answer is to use the router in modem mode and provide your own router or add a config to your pihole to divert queries for the failing domains.
This was discussed in Unable to get to gov.uk domain when using PiHole & Unbound - #7 by i7andy
Same here. With me it happened when Virgin Media changed my IP address.
I now have a file /etc/dnsmasq.d/99-my-settings.conf in which I have added:
server=/**.gov.uk/1.0.0.1
server=/*.tv/1.0.0.1
and then restarted dns
(There should be a single asterisk on that first line )