Hi @Markus
I spent some time getting frustrated just like you when I tried to first reproduce your issue and then simplify the problem down to the minimal amount of code.
Then I discussed your issue with engineering it is indeed a bug in 7.6.0 classified as “Eventing subdoc operation error out with unknown macro error” due to an uninitialized variable.
The fix is already merged in the upcoming 7.6.2 release
Best
Jon Strabala
Principal Product Manager - Server