Comment 7 for bug 999985

Remmina always goes to right monitor. If I swap my monitors in the Displays config app, then Remmina goes to the new right monitor. (So it appears to have nothing to do with which monitor is primary, only which one is on the right.)

So the workaround is to set the monitor where you want Remmina as the monitor on the right side. (And even if you change which monitor is on the right after fullscreening Remmina, it will move itself to that screen.)