Truncating the KB article text to fit into Article List on Knowledge Base Portal Page may happen in the middle of a link, rendering "Show More" link invalid, containing parts of both Show More link itself and the link in the content. For this to happen, a link in the article contents has to be specifically where the truncation occurs.
The link in HTML is not accounted for as expected during content truncation.
This issue is fixed in Workflow 7.5 SP1.
For the time being, please move the link in the article towards either beginning or the end of the article content to avoid the truncation in the middle of the link.