Hello Masab Bin Nasir,
Thank you for posting in Microsoft Community forum.
How many DCs did you have in your domain?
For AD replication error 8606, you can refer to steps with possible solution in the similar thread.
Prblems with DC Replication - Microsoft Q&A
I hope the information above is helpful.
If you have any question or concern, please feel free to let us know.
Best Regards,
Daisy Zhou