I've had this happen on a couple of systems recently. It got raised to Mitel Design who fixed it on one site and a second site has been raised to design today but I haven't been told exactly what it is yet.
SDS is enabled, forms are sharing at the correct scope for Flow Through Provisioning, and all forms sync successfully except the Telephone Directory, which results in the Remote Directory Numbers form being blank. Samples of error logs below are from the system being added into the network, the number referred to is a remote phone that should sync to the remote directory numbers.
Software Log Errors:
overwriteSegmentDEIRecords() - syncTuple failed - The Telephone Number <4441> is not known locally. Synchronize Service Hosting and/or Device Level Resiliency
Maintenance Log Errors:
Cannot update or sync record # 190 for <Telephone Directory> (The Telephone Number <4441> is not known locally. Synchronize Service Hosting and/or Device Level Resiliency.)
Is this similar to what you're getting Tinos? I'm on Mitel Support guys' case to find out why this is happening so I can avoid it, their notes on the last closed ticket were not helpful.