No fill no stroke rectangle in Illustrator CC 2018 on a PC has an appearance on it and it shouldn't
When you try to make and use a no fill no stroke rectangle (in Illustrator CC 2018 on a PC) and attempt to use it to define a pattern piece or a brush (so you can create an overlap) the rectangle doesn't work! If you select it and, from the Appearance panel flyout menu, Reduce to basic appearance then it works. So, clearly some appearance is on the shape which isn't visible but which is causing it to fail. This happens on both my PCs and one of my student's PCs (they originally drew my attention to this). I can't duplicate the issue on the Mac so I think this might be a PC only issue?
Nope, not PC only. I'm an instructor in a Mac lab and so far, one of my students' computers has the same issue.