Yeah, that would check out. This logic creates the association when the widget is created, so if the camera does not exist yet, the association will fail.
This should fix the issue:
I moved the logic to find the camera and sequence to the first tick when the active sequence is playing, to guarantee it exists when setting the association.
Be warned, the Get All Actors With Tag is a very expensive function. Given its use here, I would say keep it for ease of use for your artists, but just know that it may cause a slight lag on your first played frame if there are a lot of actors in your scene, as this node has to filter through all actors in the level and check for this tag. The reason I suggest you keep it is because the alternative is having your artist manually select the camera to track, which I would not recommend.