Ajax Failing on Q&A Plugin

We have the Q&A plugin installed on our multisite network (with around 2000) sites. We are testing it out on 1 site, but it keeps having issue with voting. This is from the admin of the site:

"In my experience voting usually works, but sometimes fails on all different browsers and platforms. (And once it fails for a session, I seem to have to log out of the broswer and swap to another to get it working again.) On Safari and Chrome, when it fails the error message is about access to https://comp590discretestructures.web.unc.edu/wp-admin/admin-ajax.php"

We thought it might have something to do with domain mapping from posts likes this one: https://premium.wpmudev.org/forums/topic/voting-not-working-getting-ajax-related-error

But this site does not have domain mapping enabled on it, and all sites are set to use the default URL on the backend. Do y'all have any other idea what might be going on here to cause it to error out?