The popups for breaks sometimes only popup on one screen in networking mode. 
For instance:
* the countdown for a break pops up (on both screens) but I ignore it. At 0 it disappears at one screen (where I am working), on the other screen it keeps blinking. If I then take the break, the break popup is only on the other screen.
* I take a manual break by clicking the button in the in the timer window, only at that screen the break window pops up.
* when I postpone a break on one computer, the popup on the other computer stays (that may be ok) but if I then SKIP it on the other computer, it has only postponed and not skipped.


Also when a dual screen (extend desktop to 2nd monitor) is used, it is not visible on both screens. This makes that you sometimes dont notice that you should take a break, or it may seem that the system "hangs" for unknown reasons.

I'm getting this on Linux also. My left monitor is the first one plugged in but I use that for a standing desk and my second for sitting down. I've tried with both outputs as primary but, for periods when I am sitting down and I want to get something finished off, I'm unable to click the Skip button when the dialog box pops up on the right screen, requiring me to turn my other monitor on to click Skip then turn it off again.