Replies to comments do not nest properly

I have a visitor to this site who posts replies to comments (on pages like https://bayoucitypressbooks.com/the-maldives-is-so-much-more-part-ii/). This visitor uses the Chrome browser.

Some of her replies nest correctly beneath the comments (they have a 20px left margin). However, sometimes her replies to comments do not nest. We cannot determine why this is happening or how to fix it.

The page I need help with: [log in to see the link]