Stopped working after moving to host with PHP 8

On PHP 8

Fatal error: Uncaught TypeError: call_user_func(): Argument #1 ($callback) must be a valid callback, class “” not found in /home/deb139228/domains/me-cvsvereniging.nl/public_html/wp-content/plugins/similar-posts/common_functions.php:638 Stack trace: #0 [internal function]: ppl_do_replace() #1 /home/deb139228/domains/me-cvsvereniging.nl/public_html/wp-content/plugins/similar-posts/common_functions.php(645): preg_replace_callback() #2 /home/deb139228/domains/me-cvsvereniging.nl/public_html/wp-includes/class-wp-hook.php(303): ppl_content_filter() #3 /home/deb139228/domains/me-cvsvereniging.nl/public_html/wp-includes/plugin.php(189): WP_Hook->apply_filters() #4 /home/deb139228/domains/me-cvsvereniging.nl/public_html/wp-includes/post-template.php(253): apply_filters() #5 /home/deb139228/domains/me-cvsvereniging.nl/public_html/wp-content/themes/mecvs/template-parts/content.php(45): the_content() #6 /home/deb139228/domains/me-cvsvereniging.nl/public_html/wp-includes/template.php(772): require(‘/home/deb139228…’) #7 /home/deb139228/domains/me-cvsvereniging.nl/public_html/wp-includes/template.php(716): load_template() #8 /home/deb139228/domains/me-cvsvereniging.nl/public_html/wp-includes/general-template.php(204): locate_template() #9 /home/deb139228/domains/me-cvsvereniging.nl/public_html/wp-content/themes/mecvs/singular.php(25): get_template_part() #10 /home/deb139228/domains/me-cvsvereniging.nl/public_html/wp-includes/template-loader.php(106): include(‘/home/deb139228…’) #11 /home/deb139228/domains/me-cvsvereniging.nl/public_html/wp-blog-header.php(19): require_once(‘/home/deb139228…’) #12 /home/deb139228/domains/me-cvsvereniging.nl/public_html/index.php(17): require(‘/home/deb139228…’) #13 {main} thrown in /home/deb139228/domains/me-cvsvereniging.nl/public_html/wp-content/plugins/similar-posts/common_functions.php on line 638

on PHP 7 it are the following warnings

Warning: call_user_func() expects parameter 1 to be a valid callback, class ” not found in /home/deb139228/domains/me-cvsvereniging.nl/public_html/wp-content/plugins/similar-posts/common_functions.php on line 638

Warning: call_user_func() expects parameter 1 to be a valid callback, class ” not found in /home/deb139228/domains/me-cvsvereniging.nl/public_html/wp-content/plugins/similar-posts/common_functions.php on line 638