Thanks Mathew,
Yes, I've tried in multiple browsers and over multiple SCORM activities. It doesn't seem to be specific to certain users, since if I filter by first or last name it changes which checkboxes become clickable.
Is it always the first few checkboxes in the grid? My hunch would say it's a CSS issue somehow but I don't know enough to say so for sure. Do you have a staging site where you can try toggling the theme set on the site to see if that makes the checkboxes clickable?
It may not help, but If I do an inpsect in our SCORM reports, on a checkbox that works, the HTML looks something like the below:
<td class="cell c0" id="mod-scorm-report_r0_c0">
<input type="checkbox" value="88255:1" name="attemptid[]" id="yui_3_17_2_1_1506081942838_145"></td>