Hi,
I upgrade to 1.5.5f, but i think the error is comming after i change PHP Version to 7.1
that is from MyDEBUG fail :

PHP Warning: A non-numeric value encountered in /home/ga.....m/includes/classes/categories_ul_generator.php on line 58
zen_categories_ul_generator->buildBranch() called at [/h ... ludes/classes/categories_ul_generator.php:85]
zen_categories_ul_generator->buildTree() called at [/ho ... /includes/templates/westminster_new/templates/tpl_modules_mobile_categories_tabs.php:122]
require(/hom... /includes/templates/westminster_new/templates/tpl_modules_mobile_categories_tabs.php) called at [/home ...emplates/westminster_new/common/tpl_header.php:121]


line 58 from catefories_ul_generator.php is: $result = sprintf($this->parent_group_start_string, ($submenu==true) ? ' class="level'. ($level+1) . '"' : '' );
line 85 from categories_ul_generator.php is: return $this->buildBranch($this->root_category_id, '', $submenu);
line 122 from tpl_modules_mobile_categories_tabs is: $menulist = $zen_CategoriesUL->buildTree(true);