Simulink Library Browser shows empty content of a custom library

He guys,

we have created a library with several sub-libraries and added them to the Simulink library browser using to the following tutorials:

https://de.mathworks.com/help/simulink/ug/creating-block-libraries.html

https://de.mathworks.com/help/simulink/ug/adding-libraries-to-the-library-browser.html

The library contains all sub-libraries as subsystem blocks,which opens the associated library using a callback function.

All, except one sub-library, are created correctly and you can see all blocks of each sub-library in the SL Browser. For reasons I don't understand, the content of one sub-library is not displayed in the SL Browser. The content of this sublibrary is displayed blank. However, when I open this empty library from the SL Browser with right-click, it opens correctly and show me the correct content. This means, that this sublibrary was created correctly.

Does anyone have an idea how I can fix this error? I am at my wit's end.

Thanks everybody and with best wishes,

Lars