I have not personally seen this error, however, I was notified by WordPress.com that the following error was caused on my dashboard by. the Blockline theme:
Fatal error: Uncaught Error: Undefined constant "BLOCKLINE_URL" in /srv/htdocs/wp-content/themes/blockline/patterns/hero-1.php:46
I am not using the pro version of the theme, simply the free version. Please let me know if I can provide any further information.
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