I work with three video monitors (Windows 8.1):

1. Monitor 1: Track View
2. Monitor 2: Console View
3. Monitor 3: Piano Roll View

Monitor 3 is connected via HDMI.
When I turn off Monitor 3-HDMI (or it goes into sleep), when I turn it on again, all of Sonar windows are repositioned to monitor 1.
Hence, I have to manually reposition these windows to their original monitors.
 
I tried to press "1" to reactivate the current ScreenSet, but it seems screenset does not work for multiple monitors when the HDMI monitor is back from sleep.
 
Does anyone know if there is any solution for this?
 

I'm afraid there's no solution; the same happens for me with all programs when my HDMI display goes into sleep. All windows go to the display 1 but do not go back to HDMI when it's turned on.
It's not SONAR specific thing. Windows does it.
 
Windows 10 here.
 
 
 

When a monitor goes offline, SONAR piles all the windows on the active one(s). Only solution I know of is to close/reopen with the display back online, but a save might actually remember them piled.

Honestly, I would disable any sleep features, but saving before break may allow the close/reopen to be used.

I personally have opened projects on a single display that were last worked on two. I close the project (no save), turn on the second monitor and reopen.

Just to throw this out...
 
I had a similar situation when opening older projects. I would re-position/resize the windows to my current environment but the project and screen preset would not save the new settings. What finally worked was to undock everything that I had combined. For example, I had grouped the console, browser and PRV in the same dock. Once they were undocked, I resized each to the new size and position and then stacked (grouped) them back up.  After doing this, the screen presets saved the layout as it should and the layout was also saved in the project.
 
Just a thought.
 
 

 
I had a similar issue with a different application a year ago. It was caused by the unloading of the graphics driver when the screen was switched off and reloading the generic driver which resized the virtual screen buffer.
 
The solution involves changing a registry key for the generic graphics diver to match your monitor resolution (rather than the default VGA resolution 1024x768)
 
HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\GraphicsDrivers\Configuration\
    SIMULATED_XXXX_XXXX.....\
        0\PrimSurfSize.cx        1920
        0\PrimSurfSize.cy        1200
 
 
Here is the rather long Microsoft Technet thread with all the details...
https://social.technet.microsoft.com/Forums/windows/en-US/4d8f3aef-8c04-481b-a69a-ec0fbf3669c2/turning-off-display-resizes-open-windows
 

It did not work here. Even deleting all registry keys under "HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control\GraphicsDrivers\Configuration\", recreating all monitor configurations and setting all monitors to the same resolution, the problem persists.
 
But reading the the Microsoft Technet thread you said (https://social.technet.microsoft.com/Forums/windows/en-US/4d8f3aef-8c04-481b-a69a-ec0fbf3669c2/turning-off-display-resizes-open-windows) one post gave me the solution: use the program http://www.ninjacrab.com/persistent-windows/.
 
Now all windows remains in the same place even turning off and on the HDMI monitor! 
 
Thanks James!