Found a weird bug - and workaround

[RocketBlam]

I have a Moon lander (this is RSS), attached to a transfer stage, orbiting the moon. I disconnect from the transfer stage, which has a probe core (a HECS), batteries, an antenna and solar panels. It's definitely a legitimate probe at that point.

If I then switch to the lander... the probe disappears. Poof, no longer in game. If it's still within physics range, I can switch to it, but it does not appear on the map, and cannot be chosen as a flyable vehicle from the tracking station. It just disappears. This, as you might guess, would make it difficult to get back to Earth. Luckily I had a recent save point that I could reload to try different things.

After trying various solutions (including restarting), I tried to rename the vehicle, and reclassify it from being a "relay" to a "probe"), now it works. I can switch to the lander, and the transfer stage stays in the map view, and is a real, live vessel.

Here's the transfer stage and lander still connected, and I think you can see that it is all legit. I'm also using several mods (RSS, tweakscale, FASA, and a few others), so I'm not really asking for a solution here, but merely perhaps helping someone else who has the same problem.

 

Edited January 6, 2018 by RocketBlam

[Geonovast]

Are you sure you didn't just have relays filtered out from your tracking station?

 

[RocketBlam]

Hmm, so I did. Well, that solves it. I didn't even realize there was a new category called "relays". This explains my confusion.

[Geonovast]

Always been there for me, but I just started (relative to KSP's age)