Monitor のお話です。
まあ、下を読んでください
Release Note: BIG-IP Local Traffic Manager and TMOS version 10.2.0

LTM http, https, tcp monitors with non-empty send string need \r\n specified (CR135548-1)
When you create a new TCP, HTTP, or HTTPS monitor in version 10.2.0, you must include \r\n at the end of a non-empty Send String, for example GET /\r\n instead of GET /. If you do not include \r\n at the end of the Send String, the TCP, HTTP, or HTTPS monitor fails.

こっそり入れてくるんですよね。
SOL2167: Constructing HTTP requests for use with the HTTP or HTTPS application health monitor
このあたりを読み進めると色々問題が見えてきますよ
あ、ドキュメント自体は役に立つものなんですけどね。