now everything works again

Through several forums I learned that this may be due to the brewing unit. Now you can either break down the brewing unit and clean it all yourself and lubricate (subsequently re-Zusammmenbauen should apparently be difficult) or the brewing unit change. So cleaned machine, changed brewing unit and it works like new again!
No more coffee residue inside the machine and the coffee "pads" in the waste container are now much stronger and apparently dry.