First check if that device (seems to be a Tuya based remote scene switch/button) is not included in your Devices tab (in the mobile or web app) anymore. If it is there, remove it via the mobile/web app from the Devices tab.
If it not on the Devices tab, then power down your Homey for 15 mins. Restart Homey and check if the unknown node is gone.
No unknow node in device tab. I know about puling the plug but it sucks. Every time you do that, all the automation becomes useless. There has to be a better way.