I earned the Legend Of Acrius (Leviathan Raid) shotgun 2 weeks before Beyond Light. I had it in my inventory When Beyond Light launched and when I went to my collections I no longer had it. I have the Trophy for completing the raid but I dont have the shotgun anymore.
Collections - https://steamcommunity.com/profiles/76561198298351111/screenshots/
Triumphs - https://steamcommunity.com/profiles/76561198298351111/screenshots/
Hey,
Did you fully complete the [b][u]full quest.[/u][/b]
You may have only partially done some of the steps you have to fully unlock the guns.
Get back to me.
Thanks.