IsValidOnMaster/IsValidOnShot need to be BlueprintNativeEvents with a default C++ implementation and allow derived classes to override the function.
This is needed so that you can create custom settings classes for Jobs for feeding things like the Burn In widget.
1. Create a new Blueprint Class
2. Inherit from UMoviePipelineSetting
3. Open Window > Cinematics > Movie Render Queue
3a. Add a Job
4. Open the Config editor for a job
5. Click Settings
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-133129 in the post.