I just got triple monitors, Left is 1080p, middle is 3k res and right is 1080p. How I get around Nvidia Surr issues is I set my main monitor to a custom res because its 21:9 vs 16:19 *you shouldnt need to do that since your monitors at all 16:9*, then I make the game window mode and drag the windows across all my monitors or I use SRWE (Simple Runtime Widow Editor). This works on some games prefect like example Dirt Rally. But games like American Trucking Sim or Euro, the window will be 6400x1080p but displaying at 1920x1080 across all 3 monitors.
I know CoD Black ops 4, and Dirt Rally work by playing in window mode and dragging window or using SRWE, the res will scale. It seems older games on like DX9 or DX10 can't do it. (I also tired assetto corsa content manager to make it triple monitor, and that worked too at full res but that a mod manger for that game alone and never tested the dragging or SRWE on that game.)
As Haldi said, nvidia surr doesn't support different res. So my suggestion would be take it out the pic. Don't use it. It simply won't work.