I’ve always had this sort of issue with RTSS when using my triple 4k setup. Most of the time MSFS2020 (or 2024) will crash when I activate on screen display, however in the 10 or 15 seconds it takes to crash, the FPS will plummet to the single digits showing massive timing increases on the GPU.
I’ve no idea why 2024/2024 are so difficult for triple monitor setups. As mentioned up thread, iRacing does it really well.