Recently I updated my Vega 64 drivers from 18.5.1 to 18.12.2 and ever since when logging into a different Windows Account or when alt-tabbing in Fallout 76 my 2nd monitor (L227WT) loses signal and it does not return unless I press Win+P to switch to PC screen 1 only, then switch back to "extend", if I reboot my PC entirely, or if I disconnect the DVI cable and plug it back in. I tried the 18.2.3, and 19.1.1 drivers as well and they had the same exact behavior. I just rolled back down to 18.5.1 drivers and the issue went away entirely, so I know the issue is driver related. I've never had a single issue with this before until I updated the drivers.
Fallout 76 is the only game I've found that causes the signal loss as it causes a short split-second flicker when alt-tabbing or closing the game which seems to be normal behavior for the game. When switching windows accounts the screen just never wakes back up after it goes blank at the login screen unless I take the steps I mentioned above to fix it.
Motherboard - ASUS ROG Crosshair VI Extreme bios v6201
CPU - Ryzen 7 1800x Pstate OC 3.9GHz
GPU - Vega 64 LC
Open Loop LC on CPU and GPU
Monitors (extended) - LG 34UC79G 2560 x 1080 DP 1.4 cable, LG L227WT 1050 x 1680 (Portrait) DVI to Active DP adapter
PSU - Corsair AX860
RAM - 16GB G.Skill Flare X 3200mhz DDR4 running at 3200mhz and rated timings/power
OS - Windows 10 Pro 64bit v1809 (latest update)
Samsung 960 Pro M.2 500gb (boot drive)
2 x Samsung 850 EVO 500gb in RAID0 (Game storage)
Seagate FireCuda SSHD 2TB (Legacy - Backup)