Have you went to Security Appliance>Active Directory and double checked that the status is still a green check. It'd be a good place to start to make sure that, for some reason, the account it is using etc didn't get borked.
Adam R MS | CISSP, CISM, VCP, MCITP, CCNP, ITILv3, CMNO
If this was helpful click the Kudo button below
If my reply solved your issue, please mark it as a solution.