Unfortunately, to solve the Dropbox sync problem, I had to completely delete Enpass and set it up again with a backup.
I also have to reset all the settings in the application.
Since then, the option "Remember the location of the last used key file" no longer works.
Before my Enpass reset, I always only have to enter the master password at Enpass start, the key file was already selected.
Now after the reset, in addition to the master password, I have to click on "Select key file