@robert Hi, thank you for your careful support.
The error logs :
PHP Fatal error: Uncaught Error: Typed property wpforo\classes\Cache::$dir must not be accessed before initialization in /home6/.../public_html/wp-content/plugins/wpforo/classes/Cache.php:346
Stack trace:
#0 /home6/.../public_html/wp-content/plugins/wpforo/includes/functions.php(2374): wpforo\classes\Cache->clean(37, 'avatar', Array)
#1 /home6/.../public_html/wp-content/plugins/wpforo/classes/Members.php(1817): wpforo_clean_cache('avatar', 37)
#2 /home6/.../public_html/wp-content/plugins/wpforo/classes/Members.php(109): wpforo\classes\Members->reset(37)
#3 /home6/.../public_html/wp-includes/class-wp-hook.php(326): wpforo\classes\Members->wpforo\classes\{closure}(37)
#4 /home6/.../public_html/wp-includes/class-wp-hook.php(348): WP_Hook->apply_filters('', Array)
#5 /home6/.../public_html/wp-includes/plugin.php(517): WP_Hook->do_action(Array)
#6 /home6/.../public_html/wp-includes/user.php(1921): do_action('clean_user_cach...', 37, Object(WP_User))
#7 /home6/.../public_html/wp-includes in /home6/.../public_html/wp-content/plugins/wpforo/classes/Cache.php on line 346