I was facing the same problem of getting a blue square status (i.e. unknown) when I configure my "GET" string as
"GET /abc/def HTTP/1.0".
The status is unknown because the request is incomplete. The server is still waiting for us to press twice like what we do when we telnet to the server. The solution to this problem for me is to configure the "GET" string as follows:
"GET /abc/dev HTTP/1.0\r\n\r\n"
Basically I'm telling the health monitor to press twice (a.k.a carriage return(\r) + new line(\n)). Hope that this solution works for you (no guarantee though).
Cheers!