It looks to me like there is a small stress area in the middle of the top bare patch. It appears that some of the resin has been loosened or ejected in that area, possibly by something falling on it. Whatever happened is probably what caused the paint to come off. The fuselage flexed and the paint lost its grip. The damaged area is somewhat weaker than the rest of the fuselage. So it would be a good idea to fix it since the repair is pretty easy.

Clean the area around the break first with lacquer thinner or acetone. Next sand the area around the break to bevel it - from the inside if you can get to it (or the outside if you can't). The idea is to bevel the edges of the good fiberglass around the break area. The bevel should extend at least 1/2" beyond the damaged area. It's not necessary to sand all the way through, but the deeper the bevel, the stronger the patch. Wipe the area down with solvent a second time.

Then put a couple of patches of cloth (6-7 oz layers will be about right) and resin over the break that just cover the beveled area. You'll need to determine if the fuselage was laminated with epoxy or polyester resin if you can. If you are not sure, use epoxy.

Be sure to check the other areas where the paint is missing ... they may have areas that need repair too.

Over the years I've repaired a number of glass fuselages this way - even spliced complete nose and tail sections. None ever gave any signs of the repair afterward. Take a look at Mike Dailey's thread on rebuilding his Kwik Fli in this forum for a pictorial of how this is done.

Great looking plane. Good luck with it.

Tony