3-page checkout, existing addresses not displayed on change shipping/payment address

[lat9]

... as identified in this Zen Cart support-thread posting.

Note that that's accompanied by a PHP Notice for each pre-existing address for the customer:

[04-Jan-2023 11:15:49 America/New_York] Request URI: /zc157a_bs4/index.php?main_page=checkout_shipping_address, IP address: 127.0.0.1
#1  require(C:\xampp\htdocs\zc157a_bs4\includes\templates\bootstrap\templates\tpl_modules_checkout_address_book.php) called at [C:\xampp\htdocs\zc157a_bs4\includes\templates\bootstrap\templates\tpl_checkout_shipping_address_default.php:71]
#2  require(C:\xampp\htdocs\zc157a_bs4\includes\templates\bootstrap\templates\tpl_checkout_shipping_address_default.php) called at [C:\xampp\htdocs\zc157a_bs4\includes\templates\bootstrap\common\tpl_main_page.php:202]
#3  require(C:\xampp\htdocs\zc157a_bs4\includes\templates\bootstrap\common\tpl_main_page.php) called at [C:\xampp\htdocs\zc157a_bs4\index.php:94]
--> PHP Notice: Trying to get property 'fields' of non-object in C:\xampp\htdocs\zc157a_bs4\includes\templates\bootstrap\templates\tpl_modules_checkout_address_book.php on line 51.