"404 not found" for online experiment

Some participants (at least 6 over about 30 participants) have reported a “404 Not Found” when clicking on the link for the experiment. It works well for lot of them because I got some data. I am using MTurk to recruit the participants and they reached me out to let me know the survey was not working for them, but unfortunately I can’t help them because I have no idea about the origin of the error. Do you have some explanations for this error?