[Samba] After Windows login black screen with mouse cursor

[Tim]

Hello,

I did an update from 4.1.16 to 4.1.17 yesterday and had some problems 
with it (using sernet package). But I think it is fine now: Replication 
works so far. Samba-tool drs showrepl has no failure and I created a 
user and it was instantly available on both DCs.

This morning a lot of clients had the following issue:
They were started as usual and the users do their login. But after this 
a black screen appears where only the mouse cursor is shown. It lasts 10 
to 15min until the normal desktop appears.

First I suspected two new installed Windows updates (KB3006137 and 
KB3021917) but after deinstallation nothing changed.

I use roaming profiles via gpo and folder redirection for AppData, 
Desktop, Documents and Favorites.

One more note: One client had this two days ago with 4.1.16.

There is a failure on each client:
Event ID 5719, NETLOGON, This computer was not able to set up a secure 
session with a domain controller in domain Domain due to the following:
There are currently no logon servers available to service the logon 
request....

Is this possibly causing the headache?

Any hints are welcome.

Thanks
Tim