Well, I've been trying some things; I've been playing with Zentyal5 and the latest Win10 build and it had a connection problem (not the same but similar).
What I've done is to connect with and without the last DC (Domain component). In your case it is .lan, so you should try logging into "zentyal-domain.lan" and then "zentyal-domain". You can alternate between those until it connects. Don't ask why.. but it has worked for me this time.
It is Zentyal5 and the problem is not the same, I know... but well, you could give it a try if there is no other solution.