Cultures which work closely together, at some point, come up with insider jokes about each other. An insider joke is one which just about everyone in the one culture immediately understands. Hopefully, the spirit of these jokes is friendly and good-natured. The Americans have theirs about the Germans. And the Germans have theirs about the Americans.
“No problem” isn’t even a joke, it’s a phrase. More is not necessary, for every German who has experience working with Americans knows what another German means when they speak it: That Americans are often quite naive about a problem, about its seriousness, impact, complexity (from the German perspective).
So when Americans substitute the term ‘opportunity’ for the word ‘problem’, Germans can become a bit nervous. For many problems offer little to no opportunities. They are simply problems. And they need to be dealt with.