On our client environment we have such issue. They have microsoft moniotoring tool as well and because of that one of registry flag is changed. Because of that they see those metrics and we don't in appmon. As a compromise we have part of environment visible in Appmon with full metrics and part not. Unfortunately I don't remember this flag name and I don't have option to check it right now. What you can check as well is if dynatrace user is in proper group of permissions related to performance counters.
More detail here:
This is not related to permission issue since I have added my user to performance log users group. By default it should have captured all the metrics but its not doing so.
Is it debugEnablePerfCounterTranslationNative flag because I tried to enable this but still the issue persists.