If it doesn't appear in a search, then it is coming from inside one of your subflows.
What version of Node-RED are you using? Clicking on the id in the Debug sidebar should highlight the Subflow instance node it is coming out of to help narrow it down - although I think there was an issue with that not quite working right until recently.
So I should update to see if the problem of not being able to click to go to the subnode is solved? I need to make several updates to the system and node to be able to update nodered, I'll try that!