Blog Character Limit

When a certain small amount of characters is exceeded in a single blog post the page actually displays some code (” title=”Share on Facebook” onclick=”return !window.open(this.href, ‘Facebook’, ‘width=500, height=500’)” target=”_blank”>) and also interferes with the blog widget area.

My site is currently not published but I have noticed the same issue on other sites using this theme https://dlelectrical.co.uk/choose-dl-electrical

Does anyone know what is causing this issue?