Thanks a lot for this workaround.
In my case, I had a macro that stretched a splinemesh between two lengths along the spline (taking in a start and end length parameter), and so I simply normalised and then multiplied by the end length minus the start length. It works great.
I had previously raised a bug about the how the Get Tangent At Distance Along Spline feature is bugged here: Unreal Engine Issues and Bug Tracker (UE-61908) - hopefully that will get fixed soon, and we won’t need to rely on this workaround any more.