It looks as if you have the problems identified in WebAIM solved.
It should be noted that the problem was identified as an empty button which is not fixed by adding a title. The lack of title or label would probably be identified when/if the button had some text. Having an ID for each MAY have eliminated the need for a title or label.
Code:
<button type="button" id="cboxPrevious"></button>
is one example and should probably, as a minimum, be
Code:
<button type="button" id="cboxPrevious">Previous</button>
The reason they were not seen in the text of the page and were seen by the tool is that the surrounding div was display:none.
display:none does NOT keep some accessibility tools or Search Engines from "seeing the code" that is hidden in the background of your browser.