Create Null From Path / Changes rotation property suddenly at the end animation (trace path)

When you select Null follows path the null auto orients to the motion path by default. When you have bezier handles at the end of a path there is a good chance that the last point on the path will only have one handle pointing back along the path. About half the time this results in a change in direction or flip for a layer that orients to the motion path and it looks like this. The arrow is Shift + parented to the Null and it is pointing the wrong way.

The fix is to select the path in the timeline, select the pen tool, hold down the Ctrl/Cmnd key to change the point tool to the white arrow cursor, and draw a selection around the last vertex to select it, then hold down the Alt/Option key to change the Pen tool to the Convert Vertex tool, then click and drag on the last vertex to give the layer (the null) something to look at when it reaches the last vertex. This fix works on any motion path, you just have to use the right tools.

Stopping the move before you get to the last keyframe is kind of a sloppy way to work. That's just putting a bandaid on the problem without washing the dirt out of the cut.

It's kind of a by-product of the code that's telling it which way to orient itself. The easiest way to address it is to have your second keyframe go to 99.99% instead of 100%.