Theme version for react-bootstrap is ^1.0.0-beta.5.
From beta.5 to beta.17 no bugs occurs.
But after ^1.0.0 version upgrade layout is broken for Header DropdownMenu:


The issue maybe is related to Popover library being updated, I really dunno.
See:
react-bootstrap/react-bootstrap@1b20f1b
A quick fix:
src\assets\scss\partials\menu_menu-lite.scss
.mr-auto {
.dropdown-menu {
margin-left: -20px !important;
}
}
.ml-auto {
float: right;
.dropdown-menu {
margin-left: 20px !important;
}
}