We upgraded to 6659 yesterday, ever since then we have not been able to create O365 users (we are DirSync enabled).  On-Prem AD ID gets created fine but when it tries to create the O365 portion, we get the following error EVERY time:

Successfully created the user. , but following errors occurred.
Error in creating Office 365 user. Error occurred while executing NewUser Code: Request_BadRequest Message: Invalid value specified for property 'mailNickname' of resource 'User'. RequestId: f12d361a-7b46-4450-b4e6-6c5e9a140b68 DateTimeStamp: Sun, 03 Mar 2019 03:06:09 GMT Details: PropertyName - mailNickname, PropertyErrorCode - InvalidValue HttpStatusCode: BadRequest HttpStatusDescription: Bad Request HttpResponseStatus: Completed  Troubleshoot...

Mailbox Alias is being set via our templates (which have not changed)

We wound up building a new server today with a fresh install of 6659, manually re-created our templates, and this error is still occurring.