When making custom systems through SM mode, moons do not seem to receive a placeholder name and instead have the name "No name". Unfortunately this means that when opening the system view for every such moon, function 3060 throws an "Object reference not set to an instance of an object". This same error is also thrown when the economy screen is opened for each colony on these "No name" bodies.
Also worth noting that I like to add empty spaces in front of important systems in order to game the alphabetic sorting.
Edit: I'm also getting one instance of function 1170 "The given key was not present in the dictionary" throwing whenever I first launch the game. (I had discovered some other systems, because of the previous error the bodies in these systems did not load in, but their entries in FCT_SystemBodies were still present, throwing the key error)
SJW: Cannot reproduce.
Follow up to this post, I think the problem happened because of a combination of me changing the Star systems name as well as the name of some system bodies which confused the game when naming moons. I've made more custom systems now without problems since I've been more careful with order in which I've been doing things.
Unfortunately I don't remember the exact order that I did. I just remember naming certain moons and their parent bodies (terrestrial), changed the name of the star a couple times and the next time I loaded the game all the moons were throwing the error and the 3 surrounding systems weren't loading.
The good news is that I have fixed the problem and rescued the save. I renamed every single moon (80+...) and then "fixed" the other 3 systems by just making them custom myself, being careful about the order of operations and have had no issues.
Something I forgot to mention that is actually important: I wasn't just renaming the stars, I actually changed their spectral class, and moved the secondary component (binary system) further away than it originally was, while it had bodies orbiting it. In addition, I deleted the Sol system once I had created the new one.