Hi,
Thanks for the recommendations. The domain replication is healthy and there are no issues bringing up new DCs in other geographical sites on this domain.
The promotion fails half-way only for this one site which is the only site with a RODC. I'm left with server which is flagged as a DC in AD, but can still be signed in with the local admin account - which is the first sign of failutre. Then I get many replication failures repadmin and dcdiag. I then need to manually go through DNS and domain services to remove the failed DC as it cannot be demoted gracefully.
I can try the promotion again, but it's failed twice and takes a lot of time to undo, so just fishing for ideas as to why this one site could be failing and if it is due to the RODC, what to do about it (such as perhaps promoting to RWDC).
I'll next try using DNS1 and DNS2 on the new DC from two other geographical sites before attempting promotion again, as using the local RODC DNS does not help.
Ever come across something like this?