Notice that in this screen shot the OPC UA server is named Ignition OPC UA Server, but in the earlier diagnostics snip, the error is "Server "Ignition OPC-UA Server" does not exist" . One has a "-" the other does not.
In your tag configuration change the name of the OPC Server to match what is actually configured on the Gateway.
Your choice of visualization system has no impact on your tags, OPC connections, or other gateway config.
It sounds like you just have two different gateways, which went through different upgrade processes. You're at minimum confusing yourself and the rest of us if you keep referring to these two gateways by their choice of visualization systems (which are not mutually exclusive, I'll further add).