The regular dtCookie is a cookie used by Dynatrace RUM to track a visit over multiple requests. It is how RUM is able to group user sessions together when a user tagging rule is not defined for an application.
The HASH_dtCookie is not something I've seen before but taking a look around online, it appears that it is an method an application server uses to "prevent an attacker from guessing session ids is to build integrity into the token by adding a hash or signature to the session cookie."
This wouldn't be something that Dynatrace is doing as you can see the same thing happening with JSESSIONID. It may be a feature enabled by your app or web servers to enhance security.
