Hi there,
The issue seems to be coming from the change to flexbox w/ effectively added this CSS:
.main-navigation .inside-navigation {
display: flex;
align-items: center;
flex-wrap: wrap;
justify-content: space-between;
}
but this should be easily addressed within the customizer settings.
Can you try going to Appearance > Customize > Layout > Primary Navigation and set the Navigation alignment dropdown to “Right”?