Had an issue yesterday with a bulb I no longer needed. So I was removing it from all rules before deleting the device. One rule had no reference on the normal UI to it but if you clicked on the gear icon on the app page to look at details the device was still listed there. As it was just one rule I ended up deleting the rule and recreating the rule machine rule. Not sure why it was still on the details view. Wish I took a screen shot but I was running late for something else so I forgot to do so. Anyone else ever see this? Any other solution besides recreating the rule?
Yes, this is a thing you'll occasionally find in complicated apps like Rule Machine. Recent changes should make this less and less common, but the general advice has been that if it's not actually in use (e.g., you can't see it in any of your selections in the UI), it's safe to remove; and that un-selecting a device before removing an action or changing options that cause it to disappear is a general technique that can help prevent this. You can probably find lots of (mostly older) posts about this with a search.
If you can figure out a specific sequence of steps that led to this, it can probably be addressed; but again, it should be less common nowadays, so especially if it's an older rule, something like the above is probably what happened.