P365: Discovery not finishing, or syncs not running - "Unable to create new PowerShell session for BinaryTreePowerShellUser" (B008352)

Discovery never finishes or for a mail from file project, when trying to sync a user, the user sync job never creates any logs and the sync never progresses.

When looking at the tenant logs or jobsapp logs, you may see the following errors:

Unable to create new PowerShell session for BinaryTreePowerShellUser.

OpenError: (System.Manageme....RemoteRunspace:RemoteRunspace) [New-PSSession], PSRemotingTransportException

OR

This can be caused by MFA being enforced on the account even though you have added the admin account and PowerShell user to the exceptions in MFA policies. The workaround so far for this has been to whitelist the IP addresses used as egress points from BT applications.

The other possible cause is permissions not applying correctly to the accounts. The admin account used to connect the tenant needs to be a global administrator during the discovery phase (for mail from file projects, this happens during the initial sync for each user).  Once that has been completed, permissions can be lowered for this account. 

For the PowerShell account, you will need Exchange admin permissions at minimum (Sharepoint admin as well if Onedrive is being migrated). Ensure the appropriate permissions are applied to the Exchange admins group, and the group has not had any permissions from the default stripped.