Didn’t see this until now.

That is why the workaround with the API Version works. ;-)

It seems the default API was changed from 2.5 to 3.0 with the recent update. Even it is (not yet) in the documentation.

Here is what I did:
I inserted in the config.js

apiVersion: "2.5",

Since the problem occurred after the recent MM2 Update (and worked fine until then) it was clear, that the update has some doing in that.

Even if the 2.5 API should be down, it is working just fine.

After this change, it works (again) like charm.