Jaiess

That solved the issue. Thank you.

AD Weirdness.mp4

I've recreated the issue, as I ended up using Albert's fix originally. This is to show that it's a curve.

The dark shape, the shadow, is a shape created using the pen tool.

Hm... interesting. That seems... kind of insane that something like that has gone for 'a long time' and still hasn't been fixed. I'm trying to avoid using Illustrator, but stuff like this makes it difficult to support Affinity Designer. I guess they already have my money though. Thanks for the response Alfred.

When I try to divide these two curves, I get a bunch of lines that mess up. Why?

If I hide one instance of the symbols, they all disappear. If you take one symbol and move it below another in the layers panel, the line issue just moves. Hard to explain without demonstrating. But apparently stacking issues in AD are known, as said by @PixelPest. I think my problem has been solved as much as it's going to be solved. I think in order to avoid stacking issues, the lines behind a painted circle would simply need to just meet the circle, rather than layering behind. Thank you everyone, I really appreciate all the help. I was grumpy and upset earlier because I couldn't figure it out and man does that drive me insane. You all have been wonderful and more responsive than I expected. :')

Okay, this was SUPER helpful. New issue came up though that I can't understand. When the circles in the attached image have a color in them, the line in the background appears through 2/3rds of the shapes/circles that I created. Everything else is symmetrical, there is no blend mode on any of the circles. But, if I move the instance of the symbol down in the layers panel, the line will move with the symbol to just fill in, say the left or right circles if I moved it from the bottom. I followed the instructions that pixelpest gave to a T. I don't believe I messed up there. As you can see from the layers panel that I extended on the right, the circles are above the line in the layers panel, on all three symbols.

Instructions still unclear after further tinkering. Rotated each new symbol instance 60 degrees and -60 degrees, still didn't work as intended. Lol.

Instructions unclear, 120 degrees does not compute. If I rotate the lines 120 and -120 degrees, they look like the linked picture. Am I dumb or something?

It would be REEEEEEEEEEEALLY nice if you could actually tell me how to achieve this, without just saying 'it took me two minutes to setup'. What took you two minutes to set up? How did you set it up? What steps exactly did you take to set it up? I've been trying to figure this out for hours and I honestly want to cry. I have honestly NO CLUE how you did this, and every video online is 20 minutes of not-helpful. Please tell me the steps you took to do this. Somebody. Anybody?