After rebooting Ubuntu 16.4 if a domain user logs in immediately they are logged in using cached credentials. It takes about 60 seconds before they are successfully logged on to the domain.
If the users’ credentials are not cached on the computer then they will get an “Invalid password” message.
The network isn’t fully up when Authentication Services (AS) tries to talk to Active Directory (AD). So AS marks servers as unreachable for one minute and then looping back to check them again. The network is up about 2 seconds after AS marks the servers as unreachable.
On the Ubuntu computer