Hello Dennis,
The error occurs when you miss FRS to DFSR migration before adding the first Windows 16 DC
DFS Replication uses a compression algorithm known as remote differential compression (RDC). RDC detects changes to the data in a file and enables DFS Replication to replicate only the changed file blocks instead of the entire file.
DFS Replication is a part of the File and Storage Services role. The management tools for DFS (DFS Management, the DFS Replication module for Windows PowerShell, and command-line tools) are installed separately as part of the Remote Server Administration Tools.
Do check the below link for better understanding
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Regards,