well the IVs were random... the only thing that would be there would be the adamant nature :/
scratch that other solution I know why it's not shiny anymore. Shininess is determined by a specific person's SID, and of course the SID is different from person to person. When a pokemon is still in its egg, it relies on the trainer's SID from the current game pak, not necissarily the trainer's SID from the game it was generated in. So as soon as an egg hatches, I assume it makes a call to the currrent trainer's SID before it displays the shininess or not. (well, obviously not as soon as it hatches, since mine appeared to be shiny at first but wasn't later. This was probably because it did used to be shiny. However I'm still not completely sure.) So when I test hatched it, the egg contents were only shiny because of my platinum's SID. When it was traded to my SS, the SID was different than my platinums so the egg wasn't generated shiny. Had I hatched it before I traded it, yes it would have retained its shininess. But since I didn't, the different SID between the two games caused the contents to change in terms of shininess.
tl;dr if you trade an egg with a shiny pokemon inside to someone else's game without hatching it, it loses its shininess (unless the two players have the same trainer ID and SID)
If you want, I could RNG a shiny bagon in my SS that's shiny with an adamant nature and has 31 IVs in attack and speed. But I wouldn't be able to get that done until later today at the earliest. Anyway, I'm heading into the room now.