After doing some troubleshooting in practice range, it did not happen in the stock version of the Lewis gun. My current specialization is full left which is: Quick Aim, Slings & Swivels, Extended Mag, and Recoil Buffer. Resetting the Specialization tree fixed the issue. Setting the same Specialization made the 3X zoom bug happen again. I changed my Specialization for High Velocity Bullets instead of Quick Aim and was able to use 3X scope properly. So I believe Quick Aim is Currently bugged on the Lewis Gun.
I'm on Xbox and have the same problem. Thanks for figuring out that Quick Aim is the problem! I'll miss quick aim...
