To reproduce the problem:

1. Add a oj-menu-button with a menu slot inside a div as following:
   <div id="mydiv" ... <oj-menu-button style='width:110px;height:100%;' class="oj-button-sm" display="icons" chroming="borderless" ... <oj-menu slot="menu"

2. in javascript request full screen mode for the div mydiv:

document.getElementById("mydiv").requestFullscreen();

Issue: The menu is not shown in full screen mode.
Reason: The menu has to be created inside the containing div.

This same issue can be found using oj-messages.