Authentication, login trouble.

Question

Hello,
Part my work's domain set up is not behaving normally. This anomaly was noticed on March 11th. My co-worker connects to the network share daily from her Mac via smb:// , but starting the 11th she couldn't anymore. It's similarly true with my other coworkers
who use Mac, and also those that use Windows that are added to the domain. We use various version of OSX (10.7 - 10.10) and Windows 7, 8.
The servers of interest:
Server A: physical machine. Host the network share. Host virtual machines. Windows Server 2008 R2 Standard SP1.
Server B: virtual machine on server A. Domain Controller, and primary DNS. Windows Server 2003 SP2
Server C: virtual machine on server A. DHCP, and secondary DNS. Windows Server 2008 R2 Standard SP1.
Server D: physical machine. Has a network share that uses active directory authentication. Windows Server 2008 R2 Standard SP1.
NAS: physical device. Synology DS415+. Connected to the domain.
I am the primary manager of these machines. I haven't done any configuration changes since the end of February, when I added a new user. These machines are patched up-to-date.
Another problem with Server A is RDP'ing to it. I usually can log in using domain admin account, or .\Administrator (local account), but now have to use SERVER_A\Administrator.
Connecting to the NAS also unable to authenticate against domain accounts; I have yet to find the error logs. I do not know when the NAS started having problem authenticating. The last time I used the NAS was at the end of February.
Interestingly, the network share on Server D works with AD authentication. Other aspects of the domain seems to be working fine.
I've been searching around the internet using these keywords: Event 4625, NULL SID,  An Error occured during Logon, 0xc000005e.
I haven't found a solution. My plan is to make a new server similar to Server D, and start a new network share. But the NAS seems unrecoverable.
Please advise. Thank you.
Event viewer's security log of Server A shows audit failure of this form when trying to connect to the network share:
- <System>
  <Provider Name="Microsoft-Windows-Security-Auditing" Guid="{54849625-5478-4994-A5BA-3E3B0328C30D}" />
  <EventID>4625</EventID>
  <Version>0</Version>
  <Level>0</Level>
  <Task>12544</Task>
  <Opcode>0</Opcode>
  <Keywords>0x8010000000000000</Keywords>
  <Channel>Security</Channel>
  <Security />
  </System>
An account failed to log on.
Subject:
Security ID: NULL SID
Account Name: -
Account Domain: -
Logon ID: 0x0
Logon Type: 3
Account For Which Logon Failed:
Security ID: NULL SID
Account Name: user.name
Account Domain: ADOMAIN
Failure Information:
Failure Reason: An Error occured during Logon.
Status: 0xc000005e
Sub Status: 0x0
Process Information:
Caller Process ID: 0x0
Caller Process Name: -
Network Information:
Workstation Name: workstation
Source Network Address: 192.168.167.181
Source Port: 50683
Detailed Authentication Information:
Logon Process: NtLmSsp
Authentication Package: NTLM
Transited Services: -
Package Name (NTLM only): -
Key Length: 0

Answer 1

It is a bad Microsoft patch. Here's a writeup.
http://www.infoworld.com/article/2895900/security/microsoft-netlogon-patch-kb-3002657-woes-continue-kb-3032359-cisco-anyconnect-fix-confirmed.html