From times to times, ArcGIS Server 10.3 failed to generate token because of an error 201 detailed as Error 201 - LDAP Response read Timeout, timeout used:-1ms.
In the logs, I see that the DC used for those failed request are not complete. Only the username was sent to the LDAP server instead of the username and password.
This error is happening randomly. Most of the times the generate token service returns the token correctly.
Any idea what could be the cause of this?