OPC connection problem with Topserver ( kepware)

I have a problem establishing a connection between Ignition and Topserver using OPC UA.
I have two instances of topserver running on two different servers. One topserver instance connects no problem at all. the other refuses to connect.
I have gone through all the Topserver settings and Ignition settings for the two connections and unable to find a difference. There is no difference bewteen the two installs or versions of topserver.
we are not running a firewall.

the ignition configuration instructions say that ignition will automatically enter a certificate into the trusted clients window of the OPC UA configuration for top server. This does not happen on the faulted connection. Manualy importing the certificate does not work either.

I am at a loss what to try next.

are you receiving any error messages? If yes, what do they say? You can go to the Status page in the gateway and select OPCUA connections and see if there is a reason for the fault.