I made a resource pack, and while testing and taking screenshots for the page, I came across this:

I've double checked my PNG for errors and found none, and while the textures are loading, it seems like the default texture is loading behind the one I made.

Thanks :)

This actually may be on me, I literally could not see, but there are artifacts in my PNG that are <1% opacity that I noticed in the file preview before examining in editor again.

Yep. That's extremely odd. I have no idea how they got there, since I just took your PNG and made it my PNG. Flat process, no extra steps, certainly no opacity changing lmao.