The UE_EXPERIMENTAL macro is not used correctly in InstancedSkinnedMeshComponent.h. It should come after the 'class' keyword & before UInstancedSkinnedMeshComponent as specified in the documentation for UE_DEPRECATED.
This causes an error when compiled instead of the expected warning.
1. Open the source code for any project.
2. Add #include "Components/InstancedSkinnedMeshComponent.h" to a source code file.
3. Begin compilation
4. Observe warnings/errors
There's no existing public thread on this issue, so head over to Questions & Answers just mention UE-365552 in the post.