I have a similar case where I took 5 years for a 4 year degree. None of the companies have denied me or had their decisions be influenced by this. However they still asked me why I took longer than the expected time. In my case I had a switch between degree choices and failed a single class leading me to have a delay of 1 year in total.
Companies mainly ask where the gap is in case you were having somewhat of an abnormal reason. Such as high stress leading you to quit school for a year. Or simply going on a world trip in the middle of school. These could be red flags for companies as you might not be able to handle the position or be able to commit to the company.
However, having failed a single class should not have that large of an effect unless the market for computer science is oversaturated and they only want straight A students. Which I highly doubt.
As to the key of your question.
Should I include the leave on my resume?
NO. Your resume is made to sell yourself. Not give them reasons to pass up on you. If they believe it's important, then they will ask you during the interview. And they usually will only ask to satiate their curiosity.
On a side note. your internships are working experience, so ALWAYS add that to your resume. It should help the interviewer understand why it took you longer too.
Degree - 2014 - 2018
bla bla bla, other interesting stuff on resume
Working experience :
Internship jan-2017 ~ Jun-2017 [company name]
During my internship I used X,Y,Z technologies and I applied them by using the "A" Method, bla bla bla.
There is no mention of the leave anywhere But it's still fairly obvious you had an internship during your studies. Which may have increased time.