Membership 2 Pro Mailchimp Add-on causing errors and not working

Hi There

I contacted your support and applied a fix to issues with the mailchimp add on previously, however we have noticed that there are still issues and I have just tested and can see the following error message.

Please advised how to fix this

[17-Oct-2017 10:47:42 UTC] PHP Fatal error: Uncaught Error: Using $this when not in object context in /home/xxxxx/public_html/wp-content/plugins/membership/app/addon/mailchimp/class-ms-addon-mailchimp.php:441
Stack trace:
#0 /home/xxxxx/public_html/wp-content/plugins/membership/app/addon/mailchimp/class-ms-addon-mailchimp.php(144): MS_Addon_Mailchimp::is_user_subscribed('sallytest@test....', 'd565dbc77f')
#1 /home/xxxxx/public_html/wp-includes/class-wp-hook.php(298): MS_Addon_Mailchimp->subscribe_registered(Object(MS_Model_Event), Object(MS_Model_Member))
#2 /home/xxxxx/public_html/wp-includes/class-wp-hook.php(323): WP_Hook->apply_filters('', Array)
#3 /home/xxxxx/public_html/wp-includes/plugin.php(453): WP_Hook->do_action(Array)
#4 /home/xxxxx/public_html/wp-content/plugins/membership/app/model/class-ms-model-event.php(546): do_action('ms_model_event_...', Object(MS_Model_Event), Object(MS_Model_Member))
#5 /home/xxxxx/public_html/wp-content/plugins/membership/app/controller/class-ms-controller-frontend.php(595): MS_Model_ in /home/encorumco/public_html/wp-content/plugins/membership/app/addon/mailchimp/class-ms-addon-mailchimp.php on line 441
[17-Oct-2017 10:48:03 UTC] PHP Fatal error: Uncaught Error: Using $this when not in object context in /home/xxxxx/public_html/wp-content/plugins/membership/app/addon/mailchimp/class-ms-addon-mailchimp.php:441
Stack trace:
#0 /home/xxxxx/public_html/wp-content/plugins/membership/app/addon/mailchimp/class-ms-addon-mailchimp.php(171): MS_Addon_Mailchimp::is_user_subscribed('sallytest@test....', 'd565dbc77f')
#1 /home/xxxxx/public_html/wp-includes/class-wp-hook.php(298): MS_Addon_Mailchimp->subscribe_members(Object(MS_Model_Event), Object(MS_Model_Relationship))
#2 /home/xxxxx/public_html/wp-includes/class-wp-hook.php(323): WP_Hook->apply_filters('', Array)
#3 /home/xxxxx/public_html/wp-includes/plugin.php(453): WP_Hook->do_action(Array)
#4 /home/xxxxx/public_html/wp-content/plugins/membership/app/model/class-ms-model-event.php(546): do_action('ms_model_event_...', Object(MS_Model_Event), Object(MS_Model_Relationship))
#5 /home/xxxxx/public_html/wp-content/plugins/membership/app/model/class-ms-model-relationship.php(2609): MS_Mo in /home/encorumco/public_html/wp-content/plugins/membership/app/addon/mailchimp/class-ms-addon-mailchimp.php on line 441