I have the same problem.
FILL is set to "1".
SHADEMODE is set to "2D wireframe" (I am not using 3D for this drawing)
Viewport is not hidden.
However, I have changed the UCS. How does one correct this problem with a rotated UCS?
I tried everything from multiple posts. SHADEMODE set to 2D was the 1 setting that changed it. Mind you FILLMODE is set to 1, and UCS - World, PLAN - World... were the other settings. Why do some people just change random things at random times, just leave normal alone or go paint on a canvas.
I recently had the same issue but discovered it when I exploded a leader line. The arrow head lost it's fill but was still a solid. All the appropriate settings were correct. What solved the "Hollow" polyline and the arrow head issue was...from the VIEW pulldown----3d views----Top view. For whatever reason someone had changed the view of the drawing I was working on. Hope this helps.
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Yea; probably hard to tell exactly what the OP wanted three years ago.
I'm pretty sure there are those who would tell you to do it with Plotstyles as well.
And then you get into the whol CTB / STB controversy. This could be ong thread when all is said and done.
Thanks for chiming in!