But after redirection to account/account, session seems wiped.

You can play  with controllers to exclude extensions effect at all.
Just open controller pages/account/account and comment two rows with hooks call
i mean lines with
//$this->extensions->UpdateData();
and
//$this->extensions->InitData();

After that no one extension hooks will run. And you will be sure problem in the server configuration or in php-code.

Just add two slashes // before call.

However, the issue still persists the login completes, but the redirection loops back to the login page instead of proceeding to the account dashboard.

one of such unexpected deleting of session can be 3d-party login extensions.
Try to uninstall them completely if presents.

please check this sql-request of upgrade script.
https://github.com/abantecart/abantecart-src/blob/1.4.1/public_html/install/abantecart_database_upgrade.sql#L87

Be sure table customer_sessions presents in the database

Run this sql-query before upgrade via phpMyAdmin.
Do not forget do full backup of your cart (see database export tab in phpMyAdmin)

--
-- DDL for table `user_sessions`
--
DROP TABLE IF EXISTS `abc_user_sessions`;
CREATE TABLE `abc_user_sessions` (
    `user_id` int(11) NOT NULL,
    `token` varchar(128) NOT NULL DEFAULT '',
    `ip` varchar(50) NOT NULL DEFAULT '',
    `last_active` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
    `date_added` timestamp NULL DEFAULT CURRENT_TIMESTAMP,
    PRIMARY KEY (`user_id`, `token`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 COLLATE=utf8_general_ci;

--
-- DDL for table `customer_sessions`
--
DROP TABLE IF EXISTS `abc_customer_sessions`;
CREATE TABLE `abc_customer_sessions` (
    `customer_id` int(11) NOT NULL AUTO_INCREMENT,
    `session_id` varchar(128) NULL DEFAULT '',
    `ip` varchar(50) NOT NULL DEFAULT '',
    `last_active` timestamp NOT NULL DEFAULT CURRENT_TIMESTAMP ON UPDATE CURRENT_TIMESTAMP,
    `date_added` timestamp NULL DEFAULT CURRENT_TIMESTAMP,
    PRIMARY KEY (`customer_id`, `session_id`)
) ENGINE=MyISAM  DEFAULT CHARSET=utf8 COLLATE=utf8_general_ci;

#update menu design item
UPDATE `abc_dataset_values`
SET value_varchar = 'design/template'
WHERE row_id=3 AND value_varchar='extension/extensions/template';

#fix or prior upgrade 1.3.4->1.4.0
UPDATE `abc_blocks`
SET controller='blocks/viewed_products'
WHERE controller='viewed_products/viewed_products' AND block_txt_id = 'viewed_products';


Not all of us are dev's. There are many apps out there that provide both an easy upgrade, and a strong defense. We know because we have used them and upgrades are secure and seamless. These Abantecart upgrades have become intimidating and that should not happen. We just want to have the best products to present to our customers.

 Agree.  Feel free send us donations. This project alive because of you and code is free.

this sounds so wierd.
Upgrade script works as chain.
1. step - running SQl upgrade script (database modification)
2. running php upgrade script.
3. replacement of files with new (including file public_html/core/version.php)

If you see version 1.4.2 in the footer of your admin side, this means previous steps was successful.

Do you have some errors in the error log?
Also you can seek some records in the install/upgrade history table.

Please give us more details.

probably same issue can be with table settings

CREATE INDEX `ac_settings_idx` ON `ac_settings` (`value`(333) ASC);

Hello,

I just wanna know if it's possible to do something to embed a specific html block with a unique url link to share outside of website in 3rd parties webpages and apps.
 
is that possible?

Yes, in theory:
1. create your own controller, let's name it myBannerBlock. As example you can get method "main" from public_html/extensions/banner_manager/storefront/controller/responses/extension/banner_manager.php.
The main function of this controller to send piece of html (tpl-render of ready html-content of block) by request parameters.
2. Then create new html-banner. Get it's banner_id.
3. Insert into table url_aliases data, where `query`  =  'banner_id=123&format=html' and `keyword` = 'some_unique_your_seo_keyword'.
4. Then open browser and put url https://www.yourdomain.com/some_unique_your_seo_keyword

It's a good idea to extend functionality our native banner manager extension. Feel free to donate us for this feature :-)