Post a token here for the developers to have a look:
You didnt post allot of info but I suspect you might have run into the same issue I experienced while updating to V4 today.
Edit the file "/etc/resolv.conf", replace the "127.0.0.1" or ":::1" address with that of for example google's DNS server "8.8.8.8"
and run the upgrade again "pihole -up".
After the upgrade, you'll notice the resolv.conf file has reverted back to using 127.0.0.1 as nameserver.