Ok well I’m clearly a moron. Tried on my phone over 4G (to check local DNS), all those URLs worked fine. Reconnected to WiFi, all work fine. So I then cleared the cache of Safari on the desktop and boom — everything works there too.
It must have been from when I was initially testing the host and the cache hasn’t flushed since. Thank you so much for your help to troubleshoot and sorry for taking up your time.