Just as title says. Specifying "localhost" in the Server Address field results in "cannot find server", but specifying loopback address 127.0.0.1 does work. Hostnames that resolve to non-loopback addresses work for other servers, so I know this field is capable of accepting hostnames.

And yes- I have performed the UWP exemption specified in the setup instructions: 

CheckNetIsolation.exe LoopbackExempt -a -p=S-1-15-2-1958404141-86561845-1752920682-3514627264-368642714-62675701-733520436