Did you hack the nomad beacon before taking nomad 1? I'd assume it would go away if you didn't (its supposed to iirc, according to the description, and if it was the Blade it would've shown up immediately and not as an enemy), but if I've had nomad planets on I tend to stay away from nomad 1 until I'm prepared to throw the beacon somewhere. The only other perma-cloaked enemy things I could think of would be things under a planetary cloak (but you have a station there, so it would've been destroyed already) or a Fallen Spire signal (which I'm pretty sure can't be on nomads anyway)