I was working on a project for a client so I can't exactly share the source file, but I was able to recreate it easily. Not sure how to describe it, but here's the issue I'm having.
The shape isn't "closed".
 

O.S. is Windows 7 32-bit, Inkscape is Inkscape 1.3 (0e150ed6c4, 2023-07-21).

Every tutorial I watch either doesn't have this issue or doesn't get this complex with their paths. Any guidance is appreciated.
 

Check out the „Fill rule“ in Fill and Stroke tab „Stroke“. Perhaps upload this example file.

I've already messed around with the 2 fill rules I know of for at least an hour in addition to messing around with whatever powerstroke setting available. I admit I don't know everything about it and it's incredibly frustrating. Doesn't help that my old hardware is making Inkscape unhappy (gee wonder why?).
 

Don't know if I'm uploading the svg correctly. Again, any help appreciated.

Not very intuitive but: Take Node tool and select one node and go Path->Reverse will cure the defective rendering instantly.

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Thank you very much! That solved all the rendering problems I was having. Cheers! 

That "might" be fixed in v1.4rc. Similiar issues were fixed in v1.4beta3.