Git status is an optional feature in treemacs, so should be enabled in the layers definition in .spacemacs

(treemacs :variables treemacs-use-git-mode 'deferred)

The above works for me on a fairly recent update of Spacemacs and packages. File names are highlighted with a different colour a few seconds after changes are made. Another possible reason git status may not show in treemacs could be the theme used (if some how the faces were the same for changed and unchanged states, although this is less likely).

It should be a bug because when I freshly start up spacemacs it shows changed files just fine. But then if I refresh the tree then it shows nothing 😕