DX12 - issues with second screen

PC Specs
Dual monitor (game on 144hz, sidemonitor for whatever 60hz, both 1920x1080)
Ryzen 5 3600x
GTX 1660 Ti (game in windowed fullscreen)
16GB ddr4 XMP@3466Mhz
Steam client installed on m.2 drive shared with OS

Game runs very smooth. No longer having hidden freezes and heavy drops that I had with Vulkan. Overall for me it plays significantly better than Vulkan.

One issue for me that happens is meanwhile the game runs fluid and with no frame issues, everything else on the PC running at the same time (occasional twitch streams or anything really that uses hardware acceleration) becomes very choppy. This doesn't happen with Vulcan. Sadly on leaguestarts I'm watching streamers while playing and DX12 makes it so choppy that basically it's disruptive, so I have to keep playing with Vulkan if I plan to run anything on the second monitor

UPDATE:
I managed to completely fix it.

I had to turn OFF Vysnc and set foreground and background FPS to a preset number instead of automatic.

Hope this helps anyone who has the same issue