We have very strange issue in SS 4.13 CMS, where author names were not show up in history tab for saved record item. However it’s shows up for published item.
If you don’t have any customisations in your project which would affect this, it is probably a bug in the core versioned or versioned-admin logic.
If that’s the case, please raise an issue in the issue tracker (after checking if there is one already, of course).