Need Help: Office 365 DKIM Failure (wrong body hash)

I need some help cause I just do not know where the problem lies or even where to go to start poking around. I am getting a DKIM failure on outgoing emails from Office365. DKIM testers are reporting the DNS is working and "correct" but an actual email test gives me this error.

DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=domain.com;

 s=selector1;

 h=From:Date:Subject:Message-ID:Content-Type:MIME-Version:X-MS-Exchange-SenderADCheck;

 bh=6cMcViI/xvdQwls9H/B9ANdzy/iWUd4nbFUpj1+bQUE=;

 b=Gh+Xp3a4lg8/3qLxHn5oS6Yd4Gcs0gRD4u7ySB6tDBPAJs8ShUjHv7Mwpxt1sIEWkqZ53Dy3yjTr7mJ+qUAyceZfS5RX53KqGsGAeZK+NMjr2s25Y0IEMZj9k8y/avtnv52N1zSLN7zQdhlhLdtOuO2VrukiWPLWNJmkJNLW82Q=

Signed-by: [email protected]

Expected-Body-Hash: FFvi8Fy89gpyVQppK0NwPGY+kbjxkS0RJArPNNcp0nA=

DKIM-Result: fail (wrong body hash: 6cMcViI/xvdQwls9H/B9ANdzy/iWUd4nbFUpj1+bQUE=)

I know this is telling me either the body of the message was edited or a wrong key is being used someplace. For our organization email is flowing from Office365 to Mimecast for archiving outgoing mail. Thinking this was the issue I setup DKIM in Mimecast. Based on the selector in the header Office365 DKIM is being used but I have no idea if Mimecast is changing anything in the body to cause a hash failure. I am at a loss in where to look at this point and could use some help.

UPDATE: This is a problem happening in Mimecast. I turned off the connector to Mimecast in Office365 and I started to pass DKIM test for hashes.