If I have a sentence with several dashes between the words (typical in the German language) then I get a lot of white space. After removing the dashes hyphenation is perfect. So I start to suspect that the dashes prevent hyphenation of the whole word combination.

The blue background color in the printscreen is because I selected the text in the pdf to highlight the "holes" in the section with the dahes. The other section contains the same words, but the dashes removed

1. zz.JPG‎ 95.4 kB

Edited 25 May 2019 by thomasdumm

This is the text to test:

Die Koronarangiografie ist in der Diagnostik der koronaren Herzkrankheit (KHK) Gold-Standard. Daneben gibt es mehrere etablierte, nicht-invasive Untersuchungsmethoden. Dazu gehören die Fahr­rad-Ergometrie, Echokardiografie (Echo), Myokard-Perfusion-Szintigrafie (MPS), Computertomografie (CT) und die kardiale Magnetresonanztomografie (MRI).

Can you post the html behind the text? how do you create it?

While putting together demo data, I found out what is causing the "holes" in the third line. I had set

hyphenate-lines: 2

which was correctly preventing the hyphenation in the third line. So my mistake