About This HTML Issue
The href value on the <a> element contains a literal < character, which is not allowed in a URL path.
The URL standard does not allow a raw < anywhere in a URL. Escaping it as < does not help, because the HTML parser turns < back into < before the URL is read. If a path really needs the character, write it as %3C.
A value that starts with part of a tag, such as <div class=, means a template or content filter wrote HTML where a URL belongs. Lazy-loading and video embed plugins can do this when they swap a video URL for placeholder markup without checking whether the URL sits inside an attribute. The first " in that markup closes the href, so the value stops at class= and the browser treats it as a relative path to a page that doesn't exist.
The rest of the injected tag spills into the <a> start tag as broken attributes. That's why the validator usually also reports a stray end tag and a quote in an attribute name for the same link. Those errors go away once the href holds a plain URL.
Other values with a < come from angle brackets copied along with an address, as in <https://www.example.com/> from a plain-text email, or from placeholders like /files/<name>.pdf left in a template. Remove the brackets or fill in the real value.
Invalid example
<a href="<div class="video-embed" data-src="https://www.example.com/embed/abc123"></div>">Watch the video</a>
Valid example
<a href="https://www.example.com/embed/abc123">Watch the video</a>
Find issues like this automatically
Rocket Validator scans thousands of pages in seconds, detecting HTML issues across your entire site.