HTTPS Health Monitor Not working

your curl output doesn't show Perceptive to be returned, are you sure it is there?

as for the reply from Samir, he suggests that it might be your server doesn't like TLS1.2, but that might not be the issue.

i would start testing with openssl, do a

openssl s_client -connect [serverip]:[port]

then create the request like you did in your two examples, it should be the GET without a / at the end and ending with HTTP/1.1

then the Host and finally the connection close.

see how the server responds to that. put the output here for extra eyes.