New windows are lost (in fullscreen mode)
Got the same issue as https://forums.opera.com/topic/22718/a-new-windows-are-lost, opening additional browser windows in fullscreen mode creates them, but they are invisible. In order to see new windows you must minimize them.
Happened after update to macOS high sierra
Version: 49.0.2725.34 - Opera is up to date
Update stream: Stable
System: Mac OS X 10.13.1 64-bit