I assume both monitors are at the same resolution and scale, yes? Please try this, uninstall Start11v2, reboot immediately after uninstall finished. Re-download latest Start11v2 version. Install it, reboot immediately again. Retest it and report back. If the issue still happen. Do you have any monitor management software running in the background. If you do, just as a test, disable it, reboot and retest it.
Thank you,
Basj,
Stardock Community Assistant