Hello, I have the same issue.
In my sequence I have two keys for “Current Position on Rail”. When I play the sequence the camera should move along the rails, but it’s not.
If I choose the “CameraRig_Rail” in the outliner and change the value here the camera follows the rail. When I do this it will also update the mesh of the rail as it’s not updating when I change the spline points.
In the image bellow you can see that the camera should be in the middle of the rail but it’s at the beginning.
This worked fine the other day. Now when I started working on it again it would not work. It’s Version 4.14