ACR filter defaults to second monitor

I have a dual monitor system.  I sometimes move panels to the secondary monitor and can move them back to the main monitor at will.  That works well for me.

However,  in recent weeks, when I choose the Camera Raw filter it automatically opens in the secondary monitor (which is not fully colour managed and therefore does not give a true representation of adjustments).  I cannot manually move it to the primary monitor.

I have searched the Edit/Preferences and cannot find a way to ensure the Camera Rwas filter opens on the Main monitor. 

I am using  a Windows 10 PC with the lastest (25.3.1) version of Photoshop..

How do I ensure the Camera Raw filter defaults to the primary screen?