Hello @Terry Lee
Before migrating to windows server 2019 you should fix domain controllers issue. meantime, for migrating to server 2019 you should migrate to DFSR.
"frsevent Checks to see if there are errors in the file replication system. (Failing replication of the SYSVOL share can cause policy problems.)"
Please refer to the Warnings and Errors about Dcdiag
Repadmin.exe Assists you in diagnosing replication issues between domain controllers. This tool requires command-line parameters to run.
For more information and to download, see Repadmin.
Best Regards
Karlie
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