1º. I’m moved the default viewport of the center out of the layout with the viewport tab and now i don’t have an idea about how layout in the center, because in the main windows show orange lines in borders but no in the center.
2º. Now, i pressed in the viewport tab to hide the tab and now over the triangle to click to show the tab , i have a UE4 icon and the small button no reply to my mouse, because the icon is over the button.
I managed to encounter the same inability to maximize the viewport when hiding the tab of your active view. There are a couple of ways to fix this, and the easiest one being would be to just reset your viewport layout. Here is an image that will help you find this option. Keep in mind this will reset your entire layout to the original defaults.
Reset Viewport Layout
This should address the issue, but if you are still having problems let me know and we can try something else.