Open the comp created with the import, convert only the Track Matte layer to a Vector layer, press the U key twice to reveal all modified properties of the layer, and ensure that you only have a simple path for each part of the X. Import the AI file into After Effects as a composition retaining layer size. Above that is the original yellow X, then the Track Matte layer with a simple stroke over each X. You now have three layers in your AI file. The stroke only needs to be a couple of points wide, but you should extend the path beyond the original X on both ends. Name the layer Track Matte, remove the brush from the layer and ensure it only contains two simple paths. In your example, you need to create a new layer, copy the yellow X, and paste it into the new layer. When you need a stroke in Illustrator to become an open path in After Effects, you must use a simple stroke in AE.
