For some clips, the following icon is displayed in the upper right corner:
(Have enlarged it digitally because it is hard to see.)
It was there “suddenly”. I have already searched the manual, but unfortunately found nothing. (I plead for an overview page with all relevant symbols in Nuendo.)
Can someone please tell me what this icon is supposed to point me to?
Thank you very much for the enlightenment. 
This would indicate that you have some kind of offline processing applied to the event. Try selecting the event and press F7 to see if that’s the case?
Thank you for your answer.
I had already thought something similar. I had made all DOP permanent in between and not used the function since. But apparently Nuendo didn’t make the effect permanent in two places and marked those clips with the icon above.