I believe there is a bug in the immersive mode in Opera 44.0.2246.122883. Specifically, I'm talking about the icon that becomes available when your phone is in landscape mode, the "[ ]" on the lower-right hand side while in the "phone" interface mode in Opera. When you click this, Opera's lower and upper bar disappear, and a semi-transparent icon appears in the lower right corner of the screen. You can click on links and it will still stay in this mode when the new page loads. However, once you click the 'back' button, you will exit from this mode, and the lower and upper bar reappear.
This mode should hide the lower and upper opera bar until you click the semi-transparent icon to exit. Could someone else please try to reproduce this issue?