Header menu length / appearance

Hi,

I′m new to wordpress and checking some themes. My site contains a menu with five entries. Applying this theme the last entry always disappear. Checking it on a big computer screen the fifth entry should appear. Right? Is that a mistake within the theme?

I can order the entries by moving one entry to position one or two. Thats not a problem.

On mobile devices the menu entries disapper with small screens. Thats correct and not a problem for me. But with big screens only 4 entries appear out of 5? Lets make it 8 entries still enough space at the right side of the screen for menue entries.

Thanks for any help!