New (but not existing) opc tags fail to read values but will still write successfully

I went to add a new feature to our Ignition project running v7.9.11, but all new OPC tags that I attempt to create never resolve to a value. The new tags have a green questionmark and a NULL value. None of the existing tags have problems and are updating without issue.

I’ve tried adding tags from various devices, some of which use different drivers, as well as server tags. The behavior is the same. Dragging from the OPC window to the tag window, or creating a tag via the context menu makes no difference. Neither does changing the scanclass, or manually defining the data type.

It’s possible that this is the first time I am adding tags since upgrading from v7.6 to v7.9, but its been a while. What’s strange is that I can write successfully to these tags so the opc item path must be correct. Is there anything else I might be doing wrong?

Thank you for your time.

I discovered some additional information that might be relevant. Using the quick OPC client via the gateway web interface, I am able to make single reads of any tag. This returns correct values. However I cannot subscribe to any tags in the quick client.