I have solved the problem by direct assigning handheld menu.
As default, the primary menu would be hidden in smart phone screen. By no mean, the primary menu affected by “Max Mega Menu” still responsively shows on that mode. So, I disabled handheld menu and used only responsive primary menu for both screen modes.
Because of that, primary menu in smart phone screen is supposed to be hidden. The header therefore performs as no area of primary menu which causes text overflowing effect.
Assigning/enabling a handheld menu totally fixes the issue.