There has been a critical error on this website.

After editing the topics page, I was unable to save it. Assuming it was an internet glitch, I tried saving it again, but each time I got an unable to save error. When I disabled the plugin, I was able to save.

However, on the live site /topics/ gives the “There has been a critical error on this website.” error.

I think its a bug because when I look at the error log I see:

[03-Sep-2024 04:24:55 UTC] PHP Fatal error:  Uncaught Error: Call to undefined function is_plugin_active() in /wp-content/plugins/wp-discussion-board/includes/classes/class-ct-db-front-end.php:1289
Stack trace:
#0 /plugins/wp-discussion-board/includes/classes/class-ct-db-front-end.php(785): CT_DB_Front_End->get_custom_excerpt()
#1 /plugins/wp-discussion-board/includes/classes/class-ct-db-front-end.php(617): CT_DB_Front_End->return_table_layout(Object(WP_Query), Array)
#2 /wp-includes/shortcodes.php(434): CT_DB_Front_End->display_all_topics(Array, '', 'discussion_topi...')
#3 [internal function]: do_shortcode_tag(Array)
#4 /shortcodes.php(273): preg_replace_callback('/\\[(\\[?)(discus...', 'do_shortcode_ta...', '\n<p>This discus...')
#5 /wp-includes/class-wp-hook.php(324): do_shortcode('\n<p>This discus...')
#6 /wp-includes/plugin.php(205): WP_Hook->apply_filters('\n<p>This discus...', Array)
#7 /wp-includes/blocks/post-content.php(50): apply_filters('the_content', '<!-- wp:paragra...')
#8 /wp-includes/class-wp-block.php(519): render_block_core_post_content(Array, '<!-- wp:paragra...', Object(WP_Block))
#9 /wp-includes/class-wp-block.php(499): WP_Block->render()
#10 /wp-includes/blocks.php(2061): WP_Block->render()
#11 /wp-includes/blocks.php(2113): render_block(Array)
#12 /wp-includes/block-template.php(260): do_blocks('<!-- wp:templat...')
#13 /wp-includes/template-canvas.php(12): get_the_block_template_html()
#14 /wp-includes/template-loader.php(106): include('/home1/as/publi...')
#15 /wp-blog-header.php(19): require_once('/home1/as/publi...')
#16 /index.php(17): require('/home1/as/publi...')
#17 {main}
  thrown in /wp-content/plugins/wp-discussion-board/includes/classes/class-ct-db-front-end.php on line 1289

How do I fix this?