I just updated it, on Windows 7, to 22.214.171.124. I think the update was released on December 13, 2017.
As I had previously told you, Garmin Express (at least on Windows) does NOT auto-update or provide you with any notification that an update is available. You have to check manually.
Not sure what going up to 5.8 from 5.7 did. I haven’t seen any differences. Maybe it was to add support to the Vivoactive 3.