error on registation when hikashop plugin is enabled

-- HikaShop version -- : 4.4
-- Joomla version -- : 3.9.22
-- PHP version -- : 7.2.34
-- Error-message(debug-mod must be tuned on) -- : 0 - Using $this when not in object context

im getting the above error when Redirect Joomla registration to HikaShop plugin.
when disabled registration using default joomla everything works fine

this is the complete error

Using $this when not in object context

Call stack
# Function Location
1 () JROOT/libraries/src/Application/CMSApplication.php:370
2 Joomla\CMS\Application\CMSApplication::getMenu() JROOT/libraries/src/Application/SiteApplication.php:275
3 Joomla\CMS\Application\SiteApplication::getMenu() JROOT/templates/purity_iii/html/com_hikashop/user/form.php:45
4 include() JROOT/libraries/src/MVC/View/HtmlView.php:701
5 Joomla\CMS\MVC\View\HtmlView->loadTemplate() JROOT/administrator/components/com_hikashop/helpers/helper.php:2512
6 hikashopView->loadTemplate() JROOT/libraries/src/MVC/View/HtmlView.php:230
7 Joomla\CMS\MVC\View\HtmlView->display() JROOT/administrator/components/com_hikashop/helpers/helper.php:2480
8 hikashopView->display() JROOT/components/com_hikashop/views/user/view.html.php:22
9 userViewUser->display() JROOT/libraries/src/MVC/Controller/BaseController.php:672
10 Joomla\CMS\MVC\Controller\BaseController->display() JROOT/administrator/components/com_hikashop/helpers/helper.php:2218
11 hikashopController->display() JROOT/components/com_hikashop/controllers/user.php:200
12 userController->form() JROOT/libraries/src/MVC/Controller/BaseController.php:710
13 Joomla\CMS\MVC\Controller\BaseController->execute() JROOT/administrator/components/com_hikashop/helpers/helper.php:2196
14 hikashopController->execute() JROOT/components/com_hikashop/hikashop.php:92
15 require_once() JROOT/libraries/src/Component/ComponentHelper.php:402
16 Joomla\CMS\Component\ComponentHelper::executeComponent() JROOT/libraries/src/Component/ComponentHelper.php:377
17 Joomla\CMS\Component\ComponentHelper::renderComponent() JROOT/libraries/src/Application/SiteApplication.php:194
18 Joomla\CMS\Application\SiteApplication->dispatch() JROOT/libraries/src/Application/SiteApplication.php:233
19 Joomla\CMS\Application\SiteApplication->doExecute() JROOT/libraries/src/Application/CMSApplication.php:196
20 Joomla\CMS\Application\CMSApplication->execute() JROOT/index.php:49

strange thing is that it works fine on php 7.0.

what could be the problem?

thanks

Hi,

The error comes from the file templates/purity_iii/html/com_hikashop/user/form.php
That file is a view override from an old version of HikaShop, either done by you or your template provider.
You can rename that view override in order to use the default view file of HikaShop and you should not have that error anymore.