It's the 21st century, and covid has unfortunately introduced a host of novel ways to cheat. It's possible that your testing content is leaked to a website where others do the work and post the answer for others to claim as their own. Due to number variation only the answer may offer limited help to most students, but is still an infringement of student honor code integrity.
If you find content from your class on a cheating site, see if there's a way to let them know it's copyrighted and to take it down lest there be a lawsuit. Chegg offers a form to email in:
Quest is working on a way to sweep the web and automatically send these notices out–tentatively aiming for this to roll out fall 2021. Check the What's New page in August to see if we made it!