Correct Wim, we use Sectiontools integrated sometimes for some special drawing. When I posted my issue, we took it for granted and just moved on.
I have not been able to reproduce this issue at that time, it just occurred with different files and projects. Once it occurred in the specific model/file, I was unable to solve it. Important note; I have used Sectiontools integrated multiple times without this issue during this same period. So what it caused that it broke, I really don’t know.
But I am now testing it again for a new project and I did not encouter this issues once. Yes, I updated evertime I received the update-notification and no, I did not check if it solved my “block editor” error.
Nevertheless, I consider this issue on my side solved.