shipping options no longer working properly

[shags38]

v1.5.5f OPC 2.2.0, Zone Rates Clone v155

configuration;
admin/modules/shipping ... zones method in use along with 'additional zones' and FreeOptions

zone 1 set to a standard shipping price
additional zone 2 set to Express Post price
free options set to free shipping for total > $65 (zone 1 standard shipping becomes zero)

at checkout both standard shipping and express post shipping are selectable (radio button)

handling fee in all cases is set to 0 (zero) (not left blank)

Issues;
1. free options not working as set when sales value exceeds $65 -still shows standard shipping rate
2. selecting Express Post option does nothing, i.e. standard shipping remains at shopping cart totals at bottom of checkout page

these settings were working correctly until recently, subsequent to when the site was migrated to another server (on same host) however I cannot definitively pinpoint this as the cause of these issues - the full recommended ZC method was used for the migration and all other aspects of the site work as desired -

the following myDEBUG error is thrown;

[07-Sep-2020 13:53:19 Australia/Sydney] Request URI: /index.php?main_page=shopping_cart, IP address: 193.115.124.73
#1  zones->quote() called at [/home2/admin/public_html/includes/classes/shipping.php:171]
#2  shipping->quote() called at [/home2/admin/public_html/includes/modules/shipping_estimator.php:140]
#3  require(/home2/admin/public_html/includes/modules/shipping_estimator.php) called at [/home2/admin/public_html/includes/templates/westminster_new/templates/tpl_shopping_cart_default.php:197]
#4  require(/home2/admin/public_html/includes/templates/westminster_new/templates/tpl_shopping_cart_default.php) called at [/home2/admin/public_html/includes/templates/westminster_new/common/tpl_main_page.php:253]
#5  require(/home2/admin/public_html/includes/templates/westminster_new/common/tpl_main_page.php) called at [/home2/dazzler3/public_html/index.php:97]

[07-Sep-2020 13:53:19 Australia/Sydney] PHP Warning:  A non-numeric value encountered in /home2/admin/public_html/includes/modules/shipping/zones.php on line 252

[mc12345678]

What was and now is the php version?

Likely something in the related files from ZC 1.5.6 that would help resolve that issue. I seem to recall that "problem" being resolved through a change to the zones file.