@lxs It's very hard to say what's wrong without seeing your actual project settings and actual scene setup.
Which exact version of the spine-unity runtime (name of the unitypackage, also listed in Assets/Spine/version.txt, or version in the Package Manager window) are you using?
Which Unity version?
Do you have 424 times the same skeleton with just a single material? How are they placed in relation to the camera, are they in the exact same 2D plane, or each slightly offset in depth? You could send us a minimal Unity reproduction project which still shows this issue. You can send it as a zip file to contact@esotericsoftware.com, briefly mentioning this forum thead URL so that we know the context. Then we can have a look.
