I have reported this bug in answerhub and in the now locked 4.14 preview thread (now locked).
Following 4.14 release I have further information (original thread locked )
I use very long splines to lay railway track with static mesh components for the sleepers (ties)
My project uses physics/collision for train and track.
All previews and now the release version of 4.14 corrupts the collision mesh after a certain distance ( seems to be 164 m or close to regardless of static mesh or collision used ( or the spacing set ).
I have tried multiple static meshes, UCX and simple box collisions in completely different BP on multiple vanilla projects.
The result is repeatable error.
In an effort to eliminate all my previous BP meshes etc.
I made a new BP/project following Dan Elliots Tutorial at Unreal Engine 4 Road Tool in Blueprints with Spline and SplineMesh - Part 2 SplineComponents - YouTube
The result is exactly the same with multiple sttatic mesh tests… corruption of the collision mesh after 160+ metres
There has been no problem with any BP track combination prior to 4.14
At the moment I cannot get answer hub to find my original report, when I can I will redirect to this thread
Meanwhile if anyone has any suggestions as to where best to look to get to the bottom of this