No devices using Pi-hole and no internet when router does use Pi-hole

Expected Behaviour:

Device internet traffic running through Pi-hole and ad’s being blocked

Actual Behaviour:

All my devices show up in red as “device not using Pi-hole” in the admin console network page when entering Pi-hole dns ( for me) at device level.

nslookup pi.hole returns SERVFAIL
nslookup to any other website works

When entering Pi-hole dns at router level, it appears in green as “uses Pi-hole” however I have no internet access.

in this case nslookup pi.hole works
but nslookup to any other website does not work

I am very confused. not very experienced working with raspberry pi’s


Debug Token:

I have fixed my issue by going back to an older version of my routers firmware. it seems to be an Issue specifically to do with the Netgear R7800