Textures in gLTF sometimes display black, but only on iOS

I having the same problem at a customer project, after updating to iOS/iPadOS 15. The web app runs perfectly fine on macOS and iOS/iPadOS 14.

The problem of missing textures can get resolved by rebooting the device. But after a certain amount of time the textures are missing again. So it seems that Safari on iOS 15 has an annoying memory bug.

Here is the topic I created last week: