Hi Arjan Gelderblom,
Let me go through this step by step.
When the Tangential is switched off, only Position information is created. With no rotational information, the object stays in the orientation it has.
With Tangential switched on, the spline is evaluated and a curve of the spline is used to find a orientation information for the object that carries the Align To Spline Tag. This is sometimes not possible (Euler Angle, etc.) A Raid Spline is then needed.
A Raid-spline is like a trainings-wheel on a bicycle: it stabilizes. It needs a distance to the main spline to work.
If you switch off tangential, any wanted rotation has to come from a different source. In the example above (Post #2), the rig can take the Tangential information, or it can work without. The animation information can be then inside of the first child Null. See example: Animate Null. A rig, as in this file, has different objects with different “duties”, i.e., functions/information.
Scene file:
https://www.amazon.com/clouddrive/share/0psysdFH5noCHacQUhvUp7ZDfKjzh4IIjXmNsvjPQEi
A little screen capture sketch
https://www.amazon.com/clouddrive/share/oLTimJsCscPO5CDEHV9QbxcoWHiRCNwh5WOXzrcMIEh
All the best