Lengthy code appearing on multple web pages

Please could you help me to understand why multiple pages on the website are displaying lengthy code at the botton of the page in a white block.

Pages displaying this are: About-Sampad Team, About-Board Members, About-Contact, Donate, Sponsor.

Code is displayed as:
Notice: Uninitialized string offset: 0 in /var/www/html/releases/20171215140338/wp-includes/class-wp-query.php on line 3152 Call Stack: 0.0000 243712 1. {main}() /var/www/html/releases/20171215140338/index.php:0 0.0001 244176 2. require('/var/www/html/releases/20171215140338/wp-blog-header.php') /var/www/html/releases/20171215140338/index.php:17 0.0794 4662600 3. require_once('/var/www/html/releases/20171215140338/wp-includes/template-loader.php') /var/www/html/releases/20171215140338/wp-blog-header.php:19 0.0820 4701104 4. include('/var/www/html/releases/20171215140338/wp-content/themes/sampad/page.php') /var/www/html/releases/20171215140338/wp-includes/template-loader.php:74 0.2200 5440160 5. have_posts() /var/www/html/releases/20171215140338/wp-content/themes/sampad/page.php:6 0.2200 5440208 6. WP_Query->have_posts() /var/www/html/releases/20171215140338/wp-includes/query.php:767 0.2200 5440472 7. WP_Query->rewind_posts() /var/www/html/releases/20171215140338/wp-includes/class-wp-query.php:3136

Thanks.

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