Update: The issue appears to be with my child theme. When I switch back to the parent them, the menu works. What could I be missing in my child setup? Everything else seems to be working properly.
The only files in the child theme folder are:
1. style.css (full copy from parent)
2. footer.php (modified copy from parent)
3. functions.php (empty)
Check your footer.php file. It may be missing a few lines as compared to the original footer.php. You can add those missing lines in your footer.php or use the original footer.php and modify it as per your needs. I had faced exactly the same problem. Fixed it by inserting the missing lines in footer.php. It seems parent theme footer.php was modified during a recent update.