BETA version -- 5.0.1002.182

[temp123312]

Maybe you pressed Ctrl+Shift+Y accidentally?
It is "Включить/Отключить поверх всех", listed in chrome://settings/cbManageShortcuts

Finally found reason... 
To reproduce this bug you need

1. In browser settings, make "toggle Fullscreen mode" by clicking "right mouse button" + "left mouse button"
2. Call your friend in Discord and start streaming Cent Browser window.
3. Make full screen IN, then OUT (Only by gesture rmb+lmb)
Done.