Looking at the video it looks like the first projector is attempting to change aspect ratio for the signal fed it, while the other two projectors are locked to a specific aspect ratio. Are you 100% sure aspect ratio is locked on all three projector settings and one isn't set for "auto" aspect ratio? The cause for it to change aspect ratio is that there is an in-game resolution that is different than the resolution that Nthusim was calibrated in. The Nthusim calibration is specific to a single resolution. You must use the same resolution in-game that is used in Nthusim calibration. Nthusim doesn't arbitrarily allow for different resolution from the calibrated resolution. hz setting can change but resolution can't. Without being on-site to troubleshoot, that would be my current diagnosis. I know that you've said that you've looked over all the projector settings though previously. That's why I'm really confused as to why it's doing what it's doing.
Within the Nvidia control panel make sure "Adjust desktop size and position" -> "2. Apply the following settings:" -> "Scaling" -> "Full-screen" -> "Perform scaling on" GPU -> "Override the scaling mode set by games and programs" enabled -> "Apply" button.
Even if something is misconfigured on the one of hte projectors that should force all projectors now to conform. Let me know if that helps.