Acrobat 20.6.20034.366983 on Mac OSX 10.14.6

Open a PDF with comments and select comment pane.

Select a comment with the cursor.

Press shift-K. The comment's checkbox should be checked.

Instead, nothing happens.

Press down arrow to move to next comment. The checkbox gets checked.

The reverse also holds true--when using the keyboard to uncheck a comment, the checkmark doesn't get cleared until you navigate off the comment.

In the video, the box is getting checked only when I hit the down arrow key and move to the next comment. You can also see the reverse, except one time (the comment reading "national") doesn't uncheck even when I hit down-arrow--I have to go back to it to uncheck.