For accessibility reasons (required for screen readers) links must contain a text or have description in aria-label attribute. In many use cases like yours you don’t want to add any text in a link, but instead use as image or any graphic element wrapper.
Fix it by adding aria-label="Twitter" to your a element, like
<a href="https://twitter.com/@some-name-here" aria-label="Twitter" target="_blank" rel="noopener" class="social-icon twitter grayscale"></a>