If the Exchange Online mailbox synchronization in Vision One is stuck on loading, it may be due to the mailbox already being tied to another account. If you previously provisioned Exchange Online to a different Vision One console, follow the steps outlined below to resolve the issue:

1. If you still have access to the old Vision One account where the domain is provisioned, clear the settings first on the old Vision One account.
2. If you don't have access to the account where the domain is provisioned, contact support together with the following details:
   • Vision One Account ID
   • Affected Domain
3. Once the domain has been removed from the old account, you can reprovision Exchange Online to Email Account Inventory. 

By clearing the old settings and reprovisioning the synchronization on the new account, the Exchange Online mailbox synchronization issue should be resolved.