We had to implement new workflow logic for one of the bugs that got fixed in 4.3.1 (incorrect position of Markers using Generators limited by Material ID)
For this we changed order how splines are processed.
Due to the vertex overlap in Your spline:
and the option used in the generator (Y offset) we get an malformed spline to work with.
You can use workaround - use 0 Y offset but add segment Z (-1 ) translation (You will need to change bevel mode to Extend for some generators).
Hope this helps and again, thank You for bringing this to our attention.