I am seeing this error as well. Initially it was just an error printed to the top of my site. I disabled and then saw the 4.5.17 update and applied this only to have the website a complete error on the front end so disabled again.
https://www.vaughanprint.com/
Just seeing the same on other sites on update of OMGF so rolling back to previous versions. Using the Divi Theme on all sites. Could be a conflict with that theme? Here is the error output:
Fatal error: Uncaught Error: Undefined constant "OMGF_DEBUG_MODE" in /home/customer/www/vaughanprint.com/public_html/wp-content/plugins/host-webfonts-local/includes/class-omgf.php:375 Stack trace: #0 /home/customer/www/vaughanprint.com/public_html/wp-content/plugins/host-webfonts-local/includes/frontend/class-functions.php(248): OMGF::debug('Found 2 stylesh...') #1 /home/customer/www/vaughanprint.com/public_html/wp-content/plugins/host-webfonts-local/includes/frontend/class-functions.php(161): OMGF_Frontend_Functions->detect_registered_stylesheets(Array) #2 /home/customer/www/vaughanprint.com/public_html/wp-includes/class-wp-hook.php(307): OMGF_Frontend_Functions->replace_registered_stylesheets('') #3 /home/customer/www/vaughanprint.com/public_html/wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters(NULL, Array) #4 /home/customer/www/vaughanprint.com/public_html/wp-includes/plugin.php(474): WP_Hook->do_action(Array) #5 /home/customer/www/vaughanprint.com/public_html/wp-includes/functions.wp-styles.php(57): do_action('wp_print_styles') #6 /home/customer/www/vaughanprint.com/public_html/wp-includes/class-wp-hook.php(307): wp_print_styles(false) #7 /home/customer/www/vaughanprint.com/public_html/wp-includes/class-wp-hook.php(331): WP_Hook->apply_filters(NULL, Array) #8 /home/customer/www/vaughanprint.com/public_html/wp-includes/plugin.php(474): WP_Hook->do_action(Array) #9 /home/customer/www/vaughanprint.com/public_html/wp-includes/general-template.php(3042): do_action('wp_head') #10 /home/customer/www/vaughanprint.com/public_html/wp-content/themes/Divi/header.php(27): wp_head() #11 /home/customer/www/vaughanprint.com/public_html/wp-includes/template.php(770): require_once('/home/customer/...') #12 /home/customer/www/vaughanprint.com/public_html/wp-includes/template.php(716): load_template('/home/customer/...', true, Array) #13 /home/customer/www/vaughanprint.com/public_html/wp-includes/general-template.php(48): locate_template(Array, true, true, Array) #14 /home/customer/www/vaughanprint.com/public_html/wp-content/themes/Divi/page.php(3): get_header() #15 /home/customer/www/vaughanprint.com/public_html/wp-includes/template-loader.php(106): include('/home/customer/...') #16 /home/customer/www/vaughanprint.com/public_html/wp-blog-header.php(19): require_once('/home/customer/...') #17 /home/customer/www/vaughanprint.com/public_html/index.php(17): require('/home/customer/...') #18 {main} thrown in /home/customer/www/vaughanprint.com/public_html/wp-content/plugins/host-webfonts-local/includes/class-omgf.php on line 375
There has been a critical error on this website.