Hello, try update theme and plugins :

1. Download theme with latest version "All files & Documentation" and unzip theme package to a folder :https://themeforest.net/downloads
2. Download old theme on your hosting and place on your computer (use for backup if new theme is have issues)
3. If you have customize old theme and you need save it on your computer
4. Delete old theme via FTP or backend dashboard and Upload new theme to your hosting with path : wp-content/themes/ and active new theme in backend dashboard -> Appearance -> Themes -> new theme -> active

Thank you

Archi Last version 3.1.2 new update

Hello, please send for me your FTP account for check and help, thanks

Hello,

Update replace this files to your website work again, path replace : wp-content/themes/archi/

Thanks

Hello, It's conflict with some qTranslate-x plugins, you have use for your website, I try find another solution for your website, thanks

Hello, please send your FTP account and WP admin account for check and help, reply private when post your wp admin account here, thanks

// Portfolio Filter
add_shortcode('foliof', 'foliof_func');
function foliof_func($atts, $content = null){
    extract(shortcode_atts(array(
        'all'        =>     '',
        'num'        =>     8,
        'columns'   =>     4,
        'cropimage' => 'no',
        'width'     =>     700,
        'height'    =>     466,
    ), $atts));
    $all1 = (!empty($all) ? $all : 'ALL PROJECTS');
    $num1 = (!empty($num) ? $num : 8);    
    ob_start(); ?>  
    <div class="container">
        <!-- portfolio filter begin -->
        <div class="row">
            <div class="col-md-12 text-center">
                <ul id="filters" class="wow fadeInUp" data-wow-delay="0s">
                    <li><a href="#" data-filter="*" class="selected"><?php echo htmlspecialchars_decode($all1); ?></a></li>                    
                    <?php 
                        $terms = get_terms( 'categories' );
                        if ( ! empty( $terms ) && ! is_wp_error( $terms ) ){
                            foreach ( $terms as $term ) {
                                echo '<li><a href="#" data-filter=".' . $term->slug . '">' . $term->name . '</a></li>';
                            }
                        }
                    ?>
                </ul>
            </div>
        </div>
        <!-- portfolio filter close -->
    </div>
    <div id="gallery" class="gallery full-gallery de-gallery pf_full_width <?php if ($columns == 2) {echo 'pf_2_cols'; }elseif ($columns == 3) { echo 'pf_3_cols'; }elseif ($columns == 5) { echo 'pf_5_cols'; }elseif ($columns == 6) { echo 'pf_6_cols'; }else{} ?> wow fadeInUp" data-wow-delay=".3s">
        <?php 
            
            $args = array(   
                'post_type' => 'portfolio',   
                'posts_per_page' => $num1,                
            );  
            $wp_query = new WP_Query($args);
            while ($wp_query -> have_posts()) : $wp_query -> the_post(); 
            $terms = get_the_terms( get_the_ID(), 'categories' );
            if ( $terms && ! is_wp_error( $terms ) ) : 
                $cate_name = array();
                $cate_slug = array();
                foreach ( $terms as $term ) {
                    $cate_name[] = $term->name;
                    $cate_slug[] = $term->slug;
                }                                    
                $categories_name = join( ", ", $cate_name );
                $categories_slug = join( ", ", $cate_slug );
                
            endif;
        ?>             
        <!-- gallery item -->
        <div class="item <?php echo $categories_slug; ?>">
            <div class="picframe">
                <a <?php global $archi_option; if($archi_option['ajax_work']!=false){ ?>class="simple-ajax-popup-align-top"<?php } ?> href="<?php the_permalink(); ?>">
                    
                        
                            <?php the_title(); ?>
                        
                    
                </a>
                <?php if ( has_post_thumbnail() ) : ?>
                    <?php                          
                        if ($cropimage == 'yes') {
                            $thumbnail = get_post( get_post_thumbnail_id() );
                            $image_title = $thumbnail->post_title;
                            $image_caption = $thumbnail->post_excerpt;
                            $image_description = $thumbnail->post_content;
                            $image_alt = get_post_meta( $thumbnail->ID, '_wp_attachment_image_alt', true );
                            // Crop
                            $params = array( 'width' => $width, 'height' => $height, 'crop' => true );
                            $image = bfi_thumb( wp_get_attachment_url(get_post_thumbnail_id()), $params );    
                    ?>
                            <img src="<?php echo esc_url($image); ?>" alt="<?php echo esc_attr($image_alt); ?>" title="<?php echo esc_attr($image_title); ?>" />
                    <?php    
                        }else{
                            the_post_thumbnail( 'thumb-portfolio' ); 
                        }            
                    ?>
                <?php endif; ?>
            </div>
        </div>
        <!-- close gallery item -->
       <?php endwhile; wp_reset_postdata(); ?>
    </div>
<?php
    return ob_get_clean();
}

Hello, a solution for your issue is not use "qTranslate slug plugin" and I have deactive this plugin, I have edit slug of your portfolio categories to english only, it's solution for you, thanks you