Bosch CTL636 spits a lot of steam before milk comes

Servus coffee connoisseursSince a
few days, our Bosch automatic coffee machine first spits a lot of steam with milk splashes before any milk flows into the cup. Since the drain hose is transparent, you can see that the milk is relatively quickly at the outlet nozzle, but something happens in the outlet nozzle that the milk is very late in the cup flow. Instead of 100ml only 50ml arrives.

I have disassembled and cleaned the system several times. Can it be that in the outlet unit (spare part 12004726 )is a piston that is moved? One could think it because above is a plug that is held with 2 clips.

Greetings Lukas

Had a citric acid/water solution sucked in today instead of milk. 300ml warm milk selected and then let stand 15min. Already after the 2nd time you could see success.

Automatic coffee machine works again ????