I'm trying to remake a grease pencil file and I forgot one little shading detail on the body part. I then went back to add the shading on said layer but it appears under it instead of over it. How can I fix this? See the images below. I'm 100% positive it is on the same layer.
My scenario is a bit different as I am not using grease pencil for anything except annotation, but I had a very similar problem
I am working in 2.8 and for me it worked to press
n as suggested here; instead of it saying anything about 'grease pencil', at the bottom of the 'view' tab there was an 'Annotations' drop-down.
In the drop-down was my existing annotation layer, if I added a new layer above the existing and drew on that everything stayed intact with my original annotation. Hurrah!
I would imagine that for your specific scenario (whilst working in 2.8) a better reference would be the blender docs here, but this is only if you can enter into edit mode on your grease pencil lines, which I couldn't because they belonged to the edit mode context of an object for me.