Your Site is Experiencing a Technical Issue

Yesterday I was logged in to my site as a Subscriber , upon visiting my Profile page I got a mail to the Administrator account showing this :-

When seeking help with this issue, you may be asked for some of the following information:
WordPress version 5.4.1
Current theme: Independent Publisher (version 1.8)
Current plugin: Simple Location (version 4.1.1)
PHP version 7.3.18-1+0~20200515.59+debian10~1.gbp12fa4f

Error Details
=============
An error of type E_ERROR was caused in line 37 of the file /var/www/markwaters.eu/wp-content/plugins/simple-location/templates/loc-user-metabox.php. Error message: Uncaught Error: Class ‘Post_Timezone’ not found in /var/www/markwaters.eu/wp-content/plugins/simple-location/templates/loc-user-metabox.php:37
Stack trace:
#0 /var/www/markwaters.eu/wp-includes/template.php(723): require_once()
#1 /var/www/markwaters.eu/wp-content/plugins/simple-location/includes/class-loc-metabox.php(132): load_template(‘/var/www/markwa…’)
#2 /var/www/markwaters.eu/wp-includes/class-wp-hook.php(287): Loc_Metabox::user_profile(Object(WP_User))
#3 /var/www/markwaters.eu/wp-includes/class-wp-hook.php(311): WP_Hook->apply_filters(NULL, Array)
#4 /var/www/markwaters.eu/wp-includes/plugin.php(478): WP_Hook->do_action(Array)
#5 /var/www/markwaters.eu/wp-admin/user-edit.php(716): do_action(‘show_user_profi…’, Object(WP_User))
#6 /var/www/markwaters.eu/wp-admin/profile.php(18): require_once(‘/var/www/markwa…’)
#7 {main}
thrown

I could see the Profile page but the Save button was missing ( below the Simple Location details ).