I feel like the image should be self explanatory. I'm using snap to grid for all of my operations so i've no idea why librecad thinks there's no closed contour. The construction is identical to the moon shape on the left, just mirrored. The area I want to hatch is made of two halved ellipses.
I'm on Mac OS and using ver 2.1.3 of LibreCAD
Thank you for your time. :)
Thanks for your response, Aman!
Unfortunately, I zoomed in until the program crashed, and there is no gap.
Also, I used snap-on-endpoints and snap-to-grid to draw the shape in the first place.
Luckily I found my own fix though, Previously I had been drawing half of the circle separately with the ellipse arc (axis) tool before adding the dividing line to make the crescent, but by drawing a whole circle with one use of the tool first, and then trimming off half of the circle instead of making it with the ellipse arc tool, LibreCAD seems to consider the hatch region valid.