Hi @roshantak44,
I’ve performed some cross-testing for us today on several of my sites which have the latest versions of WordPress, WooCommerce and our free Storefront theme as the only enabled software. When doing so I’ve not been able to replicate the behaviour which you describe with WooCommerce not saving tax rates.
This indicates that something on your site other than our WooCommerce plugin is having a negative effect and causing this behaviour which you are experiencing. Usually, isolated behaviour like what you describe and which has not displayed during our cross-testing can be related to code with another plugin or a theme which is causing a potential conflict of some kind.
I’d suggest carrying out a conflict test in your site to try and locate the culprit. This document below offer guidance on how to conflict test on a WordPress installation.
https://docs.woocommerce.com/document/how-to-test-for-conflicts/
If you haven’t carried out this type of testing on your site as yet it’s what we would recommend.