Did you tried disabling RUM? You can do that on Process group Edit page or disable rum in default application. This may be issue if you have custom path for your application (dynatrace is trying to place it's tag by default on root path).
Disabling RUM will disable collecting of user sessions but you will see Purepaths (server side monitoring). If this will work, you will need to reconfigure RUM configuration because of reasons I've mentioned before.