Incorrect identification of addresses and further calculation of delivery

On our site incorrectly calculates the cost of delivery for some addresses.
You need to understand the cause and correct the error.

Detailed TK here - https://docs.google.com/document/d/1030Jpa-3NSAAYd8YtvbnC0AsNb9cxPZ0gf-Me0vf_-g/edit?usp=sharing

Requirements:
- Good command of php/js
- Experience in Woocommerce

Please respond:
1. Enter your experience in PHP / Wordpress / Woocommerce
2. Orient approximately by cost and timing