Weapons being taken from my inv

[(XBOX)hackjuggler7]

Im a long term player and i had orthos prime before it needed mastery rank 12 when i get on after a few years i notice some of my weapons are missing and now require mastery rank higher than i currently have, i spent real money and time to get orthos prime and can even be seen in my player profile as max ranked with a 800 kills why did the weapon just disappear with no warning after i spent soo many hours getting it without even any compensation im very upset as that was one of my main weapons.