Server change over not correct.

Server change over not correct.

I hope someone can help me with this strange problem.
I have 6 PCs each running Zenon. There is Server 1, Server 2 and 4 clients. Each client runs a different program and the primary server communicates with the PLCs.
All projects are set up as Server 1 primary and Server 2 second.
The problem is if Server 1 is shut down.
Two of the projects do the correct thing, Server 2 becomes the new primary and communication with all PLCs continues.
However two projects do not do the switchover and Server 2 does not become the new primary so comms to the PLCs is lost.
I tried with one of the faulty projects to put Server 2 as primary and Server 1 as secondary, in this case Server 2 works correctly to communicate but when it is shut down, there is no switchover to Server 1, which suggests to me that the problem is in the switchover itself, not in Server 1 or Server 2.
I have looked closely at all projects, the 2 that work and the 2 that don't and can find no difference in the setup.
Can anyone please suggest a solution?

This is a migrated post! Originally posted on 13.10.2016 by user mjackson. Please be aware that information can be outdated.

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