Fatal error: Uncaught TypeError

Hello! I just tried updating from version 2.2.4 (running on the live site) to version 2.4.2 on our Dev site. The Dev site now fails to launch and shows the following error. Do you know how we might fix this?

Fatal error: Uncaught TypeError: OnlineOptimisation\EmailEncoderBundle\Front\FrontCore::isPostExcluded(): Return value must be of type bool, array returned in /code/wp-content/plugins/email-encoder-bundle/src/Traits/PluginHelper.php:120 Stack trace: #0 /code/wp-content/plugins/email-encoder-bundle/src/Front/FrontCore.php(58): OnlineOptimisation\EmailEncoderBundle\Front\FrontCore->isPostExcluded() #1 /code/wp-includes/class-wp-hook.php(341): OnlineOptimisation\EmailEncoderBundle\Front\FrontCore->register_hooks() #2 /code/wp-includes/class-wp-hook.php(365): WP_Hook->apply_filters() #3 /code/wp-includes/plugin.php(570): WP_Hook->do_action() #4 /code/wp-includes/class-wp.php(838): do_action_ref_array() #5 /code/wp-includes/functions.php(1343): WP->main() #6 /code/wp-blog-header.php(16): wp() #7 /code/index.php(17): require(‘…’) #8 {main} thrown in /code/wp-content/plugins/email-encoder-bundle/src/Traits/PluginHelper.php on line 120

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