"com.hierynomus.mssmb2.SMBApiException: STATUS_ACCESS_DENIED: Authentication failed ..." on authenticate call

I'm trying to connect to an SMB server using com.hierynomus.smbj v0.10.0. Connection is ok but as soon as I try to authenticate I'm getting this exception:

com.hierynomus.mssmb2.SMBApiException: STATUS_ACCESS_DENIED (0xc0000022): Authentication failed for 'USERNAME' using com.hierynomus.smbj.auth.NtlmAuthenticator@4152d38d 
    at com.hierynomus.smbj.connection.Connection.authenticate(Connection.java:194) 
    at MyTest.smbj(MyTest.java:...)

Here is the test code to see what I'm doing:

@Test
void smbj() throws Exception {
    SMBClient client = new SMBClient();
    try (Connection connection = client.connect("my-smb-server.de")) {
        AuthenticationContext ac = new AuthenticationContext("USERNAME", "PASSWORD".toCharArray(), "DOMAIN");
        Session session = connection.authenticate(ac);
        // ... do more here ...
    }
}

The SMB server and connection is perfectly fine since I'm able to connect from the same machine the test is running using multiple GUI tools (e.g. ForkLift) without any customized settings.

connection.getConnectionInfo() returns this before doing the authentication:

Successfully connected to: my-smb-server.de ConnectionInfo{
serverGuid=975b39d3-55c0-4490-84e7-80371b734ce7,
serverName='my-smb-server.de',
negotiatedProtocol=NegotiatedProtocol{dialect=SMB_2_1, maxTransactSize=8388608, maxReadSize=8388608, maxWriteSize=8388608},
clientGuid=85863c1f-0328-4c21-9a72-b3d907b23a1d,
clientCapabilities=[SMB2_GLOBAL_CAP_DFS],
serverCapabilities=[SMB2_GLOBAL_CAP_DFS, SMB2_GLOBAL_CAP_LEASING, SMB2_GLOBAL_CAP_LARGE_MTU], > clientSecurityMode=0,
serverSecurityMode=3,
server='null' }

Any help is highly appreciated.