Thank you for help. Might be, that your diagnose is correct, partially. We indeed have played with the (section) editor assignments.
According to my limited understanding the suggested SQL statement would add review assignment to the article #35. Since I need that for all missing articles and not only one, I have looked the other suggested option.
I have tried and deleted the editor assignment and re-created it (via GUI). Unfortunately that has not changed anything. Still the same problem.
Even more: I am sure that we have submitted at least one article (the last one, # 37) when the editor has been both, the full Editor and the Section editor. If my conclusion is correct, then all the subsequent submissions from now on will have thus wrong assignments (the same as #37), right?