Sprite Atlas bug on Android 6?

Hi everyone, I have an app that works fine on Pixel 4 / 3a with Android 11 and other devices. When I wanted to test my game on my tablet (Sony SGP612 Xperia Z3, android 6.0.1), I found a strange bug that you can see in the screenshot.

i did a little troubleshooting and found out that the bug only appears in graphics that i compressed with a sprite atlas. In the version before I ziped the assets in the atlases, the graphics would be displayed normally.

Attached are screenshots of my sprite atlas settings and the app as it looks normal / with the bug. Is anyone aware of the bug / does anyone know what I did wrong or how can I prevent it? Thanks in advance!

(the market share of Android 6 is 5.8% or so, otherwise I would put the storage space savings above this 5% of users ... :( && forgive me my broken English, I'm still in school: D)