One reason this could be happening is that the OPC UA connection these tags belong to has become disconnected for some reason. Is there any indication in your gateway status or logs that this is happening?
thank you for your explain. the black state don’t show normally. it only shows when I quick click the point like the video.to separate the problem from OPC UA connection, I make two new memory tag.
and it shows normal. but when I quick click the tree. it will show black and go back to normal very soon, maybe 1 second.