I tend to assume that you have moved the slider between
+ the upper part of the Mint Update window where it displays the list of available updates and
+ lower part of the Mint Update window where it offers the tabs "Description" and "Changelog"
so far down that it almost collapses with the bottom edge of the Mint Update window.
It should however be possible to locate the slider and pull it up again thus making the tabs "Description" and "Changelog" accessible again.
Have a look at the 2 screenshots. Hope they illustrate well what I had in mind. Hope they help you get your invisible tabs back.
Enlightened by Lucid Lynx, enchanted by Maya Mint, productive on Precise Pangolin's Minty sister