Dear All,
now it’s working.
Changes:
The setup in the multis was not adjusted to my battery.
Up to now everything was DC coupled and therfore the charger settings in the multis was not adopted to the LiFePO4 batteries (Fun fact: Victron calls the battery a “LiFePo4” battery. (I wrote my profile BEFORE I saw that 
)
I adjusted to LiFePO4 decreased the absorption voltage to 55.2V.
After theese changes the system started to work as expected.
The idea of checking the charger settings came from Andy (Off-grid garage)
https://m.youtube.com/watch?v=HilbXFCX3L8
Have Fun
edit: typos