I have a similar display setup to OP and the same problem.
Additional info: sometimes the monitor number in AIDA64 changes.
I would pin to for instance monitor 2, and then after a restart, hibernation or even when the monitors just wake from powersave the monitor numbers have changed. Result: 2 isn't the same monitor anymore.
It's like the order in which the monitors are detected changes and they get addressed 1-2-3-4 at random in stead of by device id.