Hello,
RealTimeCapture runs over multiple frames to generate the cubemap which can be the issue you are seeing when lighting in your scene varies drastically. This can be controlled with the CVar “r.SkyLight.RealTimeReflectionCapture.TimeSlice”.
Please keep in mind disabling this can cause performance impacts.
If you are not able to use RealTimeCapture for your use-cases, you can also trigger a recapture using the RecaptureSky() function on USkylightComponent or using the console command “r.SkylightRecapture”.
This will also cause a performance impact and please ensure that you are setting the component to SLS_CapturedScene.
Please let us know if this helps.