Already two times I have had the experience that after a ACS failed and was replaced the AD connection keeps disconnected.
I found out that the process AD client keeps executed failed. Also in the logging when you log in with ssh you see messages about failing.
I did resolve it by making sure the time was in sync with the AD controller (NTP) and I let the system guys throw away the object of the old ACS out of the AD.
restart the AD client process or reboot of the ACS made it create a new AD object and a running AD client services which led into a connected AD.
