I’m in the final stages of a long running Exchange migration from two on-premises ADDS forests and Exchange organisations to Exchange Online. The infrastructure foundations were laid out by some Kloudie colleagues some time ago. The environment has been running great for a while now, however, recently when trying to do some remote move migration batches to Exchange Online, I’ve been running into failures.
A few months ago I had the same issue and at that time I quickly found it to be related to DirSync. This project has an older deployment of DirSync with some customisation specific to this environment. That time I managed to find some duplicate attributes between the DirSync metaverse and Active Directory on-premises for the problematic users, which for the most part, was the cause of the problems. Fast forward and this week and I’m again running into some migration failures.