After Installing child domain in Windows 2012 R2 RTM causes the replication to fail.
Symptoms : Event ID 1202, 1126 and 1645
Evet ID 1202
Event ID 1126
Event ID 1645
After installing new child domain and join it to the Root domain
To show the child domain’s DNS partition enlisting use
Add child domain’s DNS to the forest
Make sure windows is full updated, After you apply Windows update the problem should be gone.
If not check the second solution:
Second: Make sure that your Child administrator and root administrator’s passwords are not identical.
Third: Make sure trust is set properly using the following command