So my first thread was deleted by Apple for some reason. Since I have an update that will be important to anyone else who is experiencing the same issue, I'm reposting with a summary of the issue and what I've found. Hopefully this one won't be deleted.
Bug #23844584 filed with a sample project.
Textures with an alpha channel created within an Xcassets atlas and applied during an SKAction "Animtate with Textures" animation loaded by using SKAction(named:) from an .sks file result in stretched/deformed textures on the sprite.
I think this is not strictly an Atlas issue because the same textures applied statically (ie: SKSpriteNode(texture: ...) ) or animated using an SKAction created in code are not stretched... it's only when they're animated with an SKAction built with the Actions Editor.
My current workaround for this is to use the Actions Editor as a sort of "playground" for SKActions to design & create the actions, then translate them manually into code in my project.
