Taskbar keeps moving?

[Boomerang Gaming]

I run four screens on my simulator, one is a 40" TV which is mounted above the other 3 22" wide screens using the display ports for the triple monitor and HDMI for the TV. On the TV the taskbar acts as desired and is central at the bottom of screen. On the triple display (5760 x 1080) the taskbar sometimes appears on the middle screen, then it suddenly moves to the centre of the left hand (angled) screen, it will occasionally move back and forth between left and centre screens. It no longer displays the taskbar across the bottom of all 3 screens, just a blank space which just reduces the screen size.

I have tried all the settings I can find, but cannot find why it moves back and forth, or how to set it to always display on the centre screen. Any ideas?