Hello!
We have two transform tracks in Sequencer: `UMovieScene3DTransformTrack` and `UMovieSceneTransformTrack`. The naming is arguably not great, but the former is specifically for a `USceneComponent` transform, while the other one is for any transform property. The reason for this is that `USceneComponent` doesn’t actually have a transform property: instead, it has three properties, `RelativeLocation`, `RelativeRotation`, and `RelativeScene3D`. We have a custom track for this to show up as one, instead of three different tracks.
So if you have a custom property of type `FTransform` to animate, use a subclass of `UMovieSceneTransformTrack` instead. In `UMovieScene3DTransformSection::BuildEntity`, this will make `bIsComponentTransform` be false, which will change the tag added to the ECS components, and which in turn will use a different traits that does handle `FTransform`.
I hope this fixes it!