PHP error

Subscribe to Comments Reloaded version 220502 threw the following error yesterday several times during the day:

2022/05/03 09:17:38 [error] 919#919: *56071 FastCGI sent in stderr: "PHP message: PHP Fatal error:  Uncaught TypeError: in_array(): Argument #2 ($haystack) must be of type array, bool given in /var/www/ultimatehackingkeyboard.com/wordpress/wp-content/plugins/subscribe-to-
comments-reloaded/wp_subscribe_reloaded.php:1540                                                                                                                                                                                                                                
Stack trace:                                                                                                                                                                                                                                                                    
#0 /var/www/ultimatehackingkeyboard.com/wordpress/wp-content/plugins/subscribe-to-comments-reloaded/wp_subscribe_reloaded.php(1540): in" while reading upstream, client: 172.68.143.254, server: ultimatehackingkeyboard.com, request: "GET /blog/2022/05/01/uhk-60-v2-productio
n-progress-3 HTTP/2.0", upstream: "fastcgi://unix:/var/run/php/php8.0-fpm.sock:", host: "ultimatehackingkeyboard.com", referrer: "https://ultimatehackingkeyboard.com/blog/2022/03/31/uhk-60-v2-production-progress-and-review"                                                 
2022/05/03 09:17:38 [error] 919#919: *56071 FastCGI sent in stderr: "_array()                                                                                                                                                                                                   
#1 /var/www/ultimatehackingkeyboard.com/wordpress/wp-includes/class-wp-hook.php(309): stcr\wp_subscribe_reloaded->subscribe_reloaded_show()                                                                                                                                     
#2 /var/www/ultimatehackingkeyboard.com/wordpress/wp-includes/plugin.php(189): WP_Hook->apply_filters()                                                                                                                                                                         
#3 /var/www/ultimatehackingkeyboard.com/wordpress/wp-includes/comment-template.php(2722): apply_filters()                                                                                                                                                                       
#4 /var/www/ultimatehackingkeyboard.com/wordpress/wp-content/themes/avada-uhk/comments.php(100): comment_form()                                                                                                                                                                 
#5 /var/www/ultimatehackingkeyboard.com/wordpress/wp-includes/comment-template.php(1554): require('...')                                                                                                                                                                        
#6 /var/www/ultimatehackingkeyboard.com/wordpress/wp-content/themes/avada-uhk/single.php(155): comments_template()                                                                                                                                                              
#7 /var/www/ultimatehackingkeyboard.com/wordpress/wp-includes/template-loader.php(106): include('...')                                                                                                                                                                          
#8 /var/www/ultimatehackingkeyboard.com/wordpress/wp-blog-header.php(19): require_once('...')                                                                                                                                                                                   
#9 /var/www/ultimatehackingkeyboard.com/wordpress/index.php(17): require('...')                                                                                                                                                                                                 
#10 {main}                                                                                                                                                                                                                                                                      
  thrown in /var/www/ultimatehackingkeyboard.com/wordpress/wp-content/plugins/subscribe-to-comments-reloaded/wp_subscribe_reloaded.php on line 1540" while reading upstream, client: 172.68.143.254, server: ultimatehackingkeyboard.com, request: "GET /blog/2022/05/01/uhk-60-
v2-production-progress-3 HTTP/2.0", upstream: "fastcgi://unix:/var/run/php/php8.0-fpm.sock:", host: "ultimatehackingkeyboard.com", referrer: "https://ultimatehackingkeyboard.com/blog/2022/03/31/uhk-60-v2-production-progress-and-review"