I have a problem with the editor for Text Blocks: In some text blocks, the text is not visible although so that modifiying is not possible. However, the page is displayed correctly.

In this picture the text is displayed correctly: https://cloud.simtechnology.com/nextcloud/index.php/s/qaN6MBx9o72cDbr

But in the following the text is not visible: https://cloud.simtechnology.com/nextcloud/index.php/s/ryHwce7xLADmmfo

Please advise how I can fix the problem.