0 timing on clicks

I have a survey with timing on each page. Some of my responses recorded zero for Timing - First Click, Timing - Last Click, and Timing - Click Count on all pages. A couple of other responses started out with clicks being recorded, but stopped recording clicks on later pages of the survey. The responses are complete, not flagged as bots, and have Timing - Page Submit values that are similar to other responses.
Could this be due to someone using assistive technology (i.e., for accessibility)? Or security software that blocks click recorders? If anyone knows, or has other guesses about what the cause might, I'll appreciate the help!