Your line is really small (1.22e-5 m). Is it normal? I have the impression that FME try to convert it to a point because of its very small length
Looks like, because the coordinates of the line are so close to each other, a tolerance causes the line to be snapping into a point feature. And point features are not allowed in the LineonAreaOverlayer.
Number of Coordinates: 2 -- Coordinate Dimension: 2
(1469669.0493342665,1389805.8701952382)(1469669.0493462486,1389805.8701975448)
Is there a parameter that can be set to not split a line that will result in an additional line being this short?
There is several possibilities.
In your case you can add a tester that allows lines above a determined length to pass: