QlikSense loses access. QlikSense service account is getting locked on AD level. User Sync Tasks not working.

Our customer always has the problem that the QlikSense service account is locked (means after the weekend where the system tries to log on several times and nobody knows why because nobody works).
The customer uses a proxy to go online. I suspect the problem here. We urgently need support. Even after multiple reinstallations or even searching for solutions in the community has not been successful)

In the UserManagement_Repository.log can be seen, that the UserDirectoryConnector in the QMC is started with an incorrect password:
 

18    20191121T092703.554+0100    ERROR    HUM-QLIKVIEW-02    UserManagement.Repository.Repository.Users.Factories.UserDirectoryFactory    19    c4cbab60-792c-4b3f-bc55-fc149f2ee228    CustomerDomain\service-account-qlikview    User input validation: A blank password is not allowed. Please enter a password.                c4cbab60-792c-4b3f-bc55-fc149f2ee228

19    20191121T092703.554+0100    ERROR    HUM-QLIKVIEW-02    UserManagement.Repository.Repository.Users.Factories.UserDirectoryFactory    19    11789ae7-4317-4a6a-87c6-510684dd5f64    CustomerDomain\service-account-qlikview    Exception while initializing LDAP://CustomerDomain.local: A blank password is not allowed. Please enter a password.                11789ae7-4317-4a6a-87c6-510684dd5f64

20    20191121T092703.555+0100    WARN    HUM-QLIKVIEW-02    UserManagement.Repository.Repository.Users.Factories.UserDirectoryFactory    19    b19b51b9-fe29-4ef6-8d0d-bd4c89ac1b77    CustomerDomain\service-account-qlikview    Setup of ActiveDirectory UDC not successful: A blank password is not allowed. Please enter a password.                b19b51b9-fe29-4ef6-8d0d-bd4c89ac1b77

21    20191121T092703.562+0100    WARN    HUM-QLIKVIEW-02    UserManagement.Repository.Repository.Users.Factories.UserDirectoryFactory    64    be33f5d5-3fcc-4120-b06c-cd5bf7f19037    CustomerDomain\service-account-qlikview    Setting up UDC of type Repository.UserDirectoryConnectors.LDAP.ActiveDirectory unsuccessful    A blank password is not allowed. Please enter a password.       bei Repository.Users.SafeUserDirectoryConnector.CallWithTimeout[T](Func`1 func, TimeSpan timeout)↵↓   bei Repository.Users.SafeUserDirectoryConnector.Setup(Logger logger)↵↓   bei Repository.Users.Factories.UserDirectoryFactory.TrySetupUserDirectory(UserDirectory userDirectory)        be33f5d5-3fcc-4120-b06c-cd5bf7f1903

Start QMC and browse to:
Start -> User directory connectors -> Connection
On Properties click on "Connection".
Go to the section of "CONNECTION":
If the service account is used to do the connection with the Domain Controller / LDAP enter the correct password credentials again for this account and click "Apply".