Bootstrap 5 (beta) - Navbar partial Override - Sticky Top Not Working - navbar

Question

I'm using the BS5 beta and I'm running into an odd problem with the sticky-top class - I'm relatively new to Bootstrap.
USE CASE
I want to customize the .navbar (and dependent classes). I created a complete copy of the navbar partial (not sure if this a best or bad practice, but I have too many changes to do it piecemeal.
I want to use the sticky-top class (the fixed-top class has the same problem)
IMPLEMENTATION
The custom navbar partial is imported after the off-the-shelf navbar partial.
Most of the other overrides are working fine.
ISSUES
Sticky-top only works if either:
I don't use a custom navbar partial - but obviously I don't want to modify the off-the-shelf partial.
I use a custom partial and hard-code the .navbar class position property to sticky (from relative).
So, I can make it work by hard-coding the position property - not the end of the world. But it seems to me that if sticky-top works with the off-the-shelf partial, it should work with the custom version. And I'd like to avoid unnecessary customizations...
Is this a beta bug or am I doing sth really backwards?
NAVBAR PARTIAL
.navbar {
display: flex;
// navbar position should be relative and
// sticky-top helper class should force navbar to be sticky
// this works with the off-the-shelf navbar partial, but not an overridden one
**position: sticky;** // modified - 2021.02.25
padding-top: $navbar-padding-y;
padding-right: $navbar-padding-x; // default: null
padding-bottom: $navbar-padding-y;
padding-left: $navbar-padding-x; // default: null
align-items: center;
flex-wrap: wrap; // allow us to do the line break for collapsing content
justify-content: space-between; // space out brand from logo
#include gradient-bg();
POSITION PARTIAL (not modified)
.fixed-top {
position: fixed;
top: 0;
right: 0;
left: 0;
z-index: $zindex-fixed;
}
NAV TAG
<!-- NAV BAR -->
<nav class="navbar navbar-light bg-light navbar-expand-xl sticky-top">
<div class="container-xl">