The error you saw means that there’s broken HTML somewhere in the page. Did you insert some code in the Text element? That is a usual cause of this issue.
If you’re sure you’ve not inserted broken HTML code in your site, it could be a result of incorrect website optimization, theme modification and/or caused by a third-party plugin. With that said, please do the following:
- If you’re using optimization plugins like W3 Total Cache and Autoptimize, please clear their caches and disable them.
- If you’re using a child theme and have added custom codes to it, switch to the parent theme to check if they’re the cause of the issue.
Please also tell us if this is happening Globally or only in a specific page then give us WordPress Admin Login URL, username and password in a Secure Note.