Herd only allowing one connection at a time

I am testing out some code and I have several sites configured in Herd. Site a.test on the backend, needs to communicate with b.test via a curl call, but when that happens, everything locks up and nothing is accessible until the requests times out. So when a.test is trying to make a call to b.test, even if I call b.test in another browser, it is locked until the other process times out. What would cause this?