EQ& Plus Extra spits sporadically when foaming milk

Our EQ6 Plus Extra Class, I have since May this year, sporadically spits times when milk foam.
She has so far produced about 1500 cups of coffee and 1000 cups of milk and works normally without problems. Since we have hard water, I have to clean often and regularly.
The milk system is flushed after each milk draw with the appliance function.
Every evening the water drawer is rinsed out as well as the brew head cleaned under running water. This vlerbelibt then to dry overnight outside, the flap and the water drawer remain open (for ventilation).
So every 7-10 days, milk hose, outlet nozzle and this rubber part on it, inserted in milk cleaner and rinsed.
Still, every now and then it has a "spit" when drawing milk foam. Have as it came back the two outlet parts also times in descaler solution inserted, then it was good again for a Zet.

Now, however, this no longer works and she starts to spit again ...
Is it possible to suck in descaler solution with the hose to clean the rest of the way to the outlet? I'm afraid that's where the problem lies...