Web shortcuts do not show icon

Web shortcuts do not show icon

When I add a Web shortcut to a profile and add an icon to it, the shortcut is displayed and working on the Android-tablet but the icon is not shown. It only shows the name and a lightgray Android icon.
I tried jpg-, png- and ico-files, different sizes from 28px to 100px.
When I started with MDM over half a year ago it was working fine but now not anymore.

Question is: What are the size and type demands exactly for an icon if there are any? Or what can be the problem otherwise?

Greetings, Jan

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