This comes to me word-of-mouth.
It seems there’s a longstanding bug/feature in the firewall routemap that causes the ipv6 localhost link to fail, and then the v4 link is tried, and succeeds. Apache is bound to both, but Windows won’t route the v6 link correctly.
There are a couple of solutions here, including turning off ipv6 in Windows. It’s probably easiest just to explicitly define “localhost” in C:\Windows\System32\drivers\hosts. Uncommment the 127.0.0.1 line:
# ::1 localhost