Survey123 being used on Enterprise 19.1 and on iPhones with Field Maps and Survey123 installed
The box is checked to tell it to use the latest version.
However, it sometimes does and most of the time does not.
inconsistent internet connection can cause this. I've encountered the same thing and a quick update, refresh for field users on their respective devices have always resolved this quickly enough. It could be a bug that's version or OS specific, have you checked the documentation or logs for this? If it's not an obvious bug you could always open a support ticket with ESRI.
Hope this helps,