The 'FullAccess' permission is Inherited instead of being applied directly to the user's mailbox.

Inherited Permissions Example:
Full Access for the Source Acct: edp\ExchSourceAcct

Apply 'FullAccess' permissions directly to the mailbox to be collected.
NOTE:  The below commands must be run in the Exchange Management Shell on the Microsoft Exchange Server

To view current mailbox permissions on a single mailbox
get-mailbox -Identity Adam.Coleman@edp.lab | Get-MailboxPermission -user < Insert eDP Exchange Source Account >

If IsInherited is True, the direct 'FullAccess' needs to be applied

*** IMPORTANT NOTE ***
The account of which eDiscovery Platform (eDP) will be using to access the mailbox must have a mailbox on the Exchange server or else the same permissions error will still be shown in the report log.

To Add 'FullAccess' permission directly (not through inheritance) to a single user mailbox
Get-Mailbox -Identity < user email address > | Add-MailboxPermission -User < eDP Exchange Source Account > -AccessRights fullaccess -InheritanceType all

To Add 'FullAccess' permission directly to all user mailboxes
Get-Mailbox -ResultSize unlimited -Filter {(RecipientTypeDetails -eq 'UserMailbox')} | Add-MailboxPermission -User < Insert eDP Exchange Source Account > -AccessRights fullaccess -InheritanceType all -AutoMapping:$false