Ytong adhesive applied too little - Is this a defect/to be fixed?

Statically, I wouldn't worry about that in the case of a bungalow; I would view it more critically for a multi-story building. Ignoring the processing instructions makes me concerned for a different reason: as an indication that the masonry was done by an assistant.

Yes, I now also see it as more concerning. We are also talking about 2 1/2 stories.