White/black artwork in media_player


I am developing a media_player component for the Cambridge Audio CXNv2 (https://www.cambridgeaudio.com/en/products/cx/cxn-v2)
I can request the artwork from the currently playing song. In most cases this is displayed correctly within Home Assistant. However, when using Roon, the artwork is not diplayed, all I see is a white or black square (depending on if i use the regular Media Control, or Mini Media Player.)

Here are 2 examples: one is working, one is obviously not:

URL look like this: https://static.airable.io/71/97/900708.png

URL looks like this: http://xxx.xxx.xxx.xxx/album-art-3514?id=2:96

When looking at the HTML code in both cases, I see a base64 encoded jpg or png image that can be decoded by this website for example: https://onlinejpgtools.com/convert-base64-to-jpg

Any idea what might cause this behaviour?