Root cause: automatic update on windows did not work. Version from Windows Appstore causes the problem.
Solution:
1. create local Backup with Enpass
2. deinstall Enpass
3. download an install it from (https://dl.enpass.io/stable/windows/setup/6.4.0.631/Enpass-setup.exe)
!!!! Do not use Microsoft APP Installation --> this version does not work properly !!!!
4. open backup with Enpass to restore your data
5. connect to your iCloud account
6. try to sync now with your iCloud account. If there appears a time stamp, everything works as it should.