There was a rework of pausing/resuming of external profilers in https://github.com/EpicGames/UnrealEngine/commit/33ef583ba5122c804792fecc480b14bee9fba11a
The result of this though is that `FActiveExternalProfilerBase::bIsRecording` defaults to false and there is no code path that is utilised in stock UE that enables this. This means events never get emitted due to the check against it in `FExternalProfilerTrace::StartScopedEvent`.
Steps to Reproduce
Run the game with -pix or -superluminal. Observe how scoped events are not recorded.
Thanks for the report, this flag was introduced to support custom profilers that might be expensive and only want to record for short periods, but still want to be enabled on the command line.
The disabling of profilers like PIX and Superluminal was unintentional and another engineer is going to submit a change to default bIsRecording to true and allow external profiler implementations to report that they should start disabled.
I’ll update this issue when that change is submitted.