Without diving into the sphere geometry code, and it’s been a couple years since i read it, I believe it could be the edges of the geometry that is not connected.
The sphere is created like a lathe, and it looks like (on your pictures) it’s the starting and ending edges meeting and they’re not connected, the middle points where they “connect” are duplicated rather than shared.
I’m merely guessing though.
I’ll see if i have time to dig out some old geometry cleaning code later, in the mean time, give me a couple minutes and i’ll share a sphere mesh you can try (i don’t have fusion 360)
@aWeirdo – Sorry, I’m having a bit of a hard time loading the .babylon files at the moment (apologies for that!) - would you be kind enough to export the STLs for me to try them into Fusion? I simply use this line for the STL export: