I’ve found the same problem. Attached is a zipped project that demonstrates it.
To reproduce the bug, simply open NewMap, select the SplineBug object therein, and press the Print Distances button. The Output Log should display that the “Sum of Delta Distances” is 1438.82, and that the “Actual Spline Length” is 1438.80. Scrolling up to “Current Time: 0.986” should show a Delta Distance Ratio of 1.46.
The PrintDistances function sums up the series of distances between discrete points on the spline - points which should be evenly spaced apart - and prints that sum, along with other data about the points themselves. For example, each Delta Distance Ratio describes how far these points are from actually being evenly spaced. If a point has a DDR of 0.95, it is only 95% as far away as one would expect from the previous point. If it has a DDR of 1.10, it’s 110% as far away as one would expect.
If you play with the points a lot and heavily distort the tangents - which appear to be the source of the problem - you should be able to get somewhat greater inaccuracies. These don’t seem significant in aggregate, but individually, a DDR of 1.46 (or worse!) can cause problems. In my case, I’ve been trying to have an enemy follow the spline over time, but fall off of it when it becomes de-synced with its expected position, i.e. if the player knocks it out of the way. However, this is occurring without any external interference, causing jittery movement as the enemy tries to return to the spline upon which it’s already standing.