By default, curl will send an HTTP 1.1 formatted request including a host header. It's possible that the web server isn't handling your HTTP 0.9 (GET /APP1/INDEX1/INDEX) without a host header. You could try using a host header name in the send string:
GET /APP1/INDEX1/INDEX\r\nHost: \r\nConnection: Close\r\n
You can also check the access log on the server to see what request and/or response is being sent/received. You can also enable debug on the monitoring daemon bigd to see the request and response send/received for the monitoring. You can enable debug from the command line using 'b db bigd.debug enable' and disable it using 'b db bigd.debug disable' . It does create very large output files (/var/log/bigd.debug).
You could also use tcpdump and filter on the non-floating self IP address and the server IP address:port:
tcpdump -ni SERVER_VLAN -s0 -w/var/tmp/`/bin/hostname`.monitor.dmp host LTM_STATIC_IP and host SERVER_IP and port SERVER_PORT
You would need to use ssldump to decrypt the trace though, so bigd debug might be easier to check with.
Aaron