Hello and welcome to the Babylon community!
Since the GUI can be affected by post-processes, and we have glow and highlight here, I feel they might be the culprits. If you remove them, does that problem still happen? If that solves the problem and you want to add the glow and highlight, you’ll just need to have a separate camera for the GUI: How to make gui disable in DefaultRenderingPipeline? - Questions - Babylon.js (babylonjs.com) How to disable post effect on GUI that linkWithMesn - Questions - Babylon.js (babylonjs.com)