MMEx 8.12 Exchange 2010 SP3 source and target.
Getting reports of migrated users seeing the From field on some email as being blank/empty (outlook & OWA). The data is in the header, and it’s not all of the emails. It also doesn’t affect the new emails arriving since the mailbox was migrated. I’ve migrated a few hundred mailboxes prior to this issue. This is a different physical site with separate Admins though, so anything’s possible. I found a couple Quest articles around the issue, but Exchange is patched to RU15, and the MM is a version that shouldn’t be affected.
https://support.quest.com/migration-manager-for-exchange/kb/107029
FYI. I did have an issue last week, where users were missing some emails so I did a full re-sync. I wouldn't think that's related, but just in case.