These contain useful information - if the injection was tried and what was the result. In this example, RUM was injected by an application server and also tried on the webserver, but it was already injected.
A lot of RUM injection errors can be diagnosed this way.
if the agent is deployed and application processes restarted
if you have remaining DEM licenses in your environment as injection won't happen if there are no remaining DEM licenses
check your application detection rules in Settings > Web and mobile monitoring > Application detection and check if the application URL resolves to the desired application in Dynatrace
check if the Application in Dynatrace is enabled
check if injection for the process groups where it should happen is enabled
some Java web frameworks (ZK framework for example) already produce compressed output and Dynatrace is unable to inject there. You can try to issue the request without Accept-Encoding header and check if the injection is performed or not.
Some built-in Java webservers such as undertow in certain combinations have issues with injection. Try setting the Deep Monitoring flag "Java Real user monitoring v2" for the process groups.