Deleting multiple comments - "Remove Highlights and Comments" greyed out

Using Numbers 3.6.1 on a MacBook Pro (13" retina, late 2013).

I want to remove all comments on several hundred cells at once (amongst the cells with comments are some without) without affecting the contents of the cells - for that, the command "Remove Highlights and Comments" would seem ideal... but it is permanently greyed out, seemingly regardless of what I do. The only way I have found to delete a comment is to use the delete button for that purpose inside the comment window... which then closes, leaving no cell selected, so I have to repeatedly select the next cell with the mouse, renavigate to the button, press and... wait.

I've looked in the 'Help', searched the web, this database too, and found nothing helpful. Now maybe I'm overlooking something, maybe because I have been using Numbers and its predecessors, as well as Excel on Windows (and Lotus 1-2-3 before that in DOS), for multiple decades something obvious is staring me in the face... whatever, am hoping for your help!