Do other aspects of the dark themes remain the same? Just eh text is hard to see?
Can you test:
Open home directory and ensure that all hidden files are showing with ctrl+h
Right click /.config
Rename it to /.config-bkp
Log out and back in. Test themes.
If that works, then it is likely something in a config file, perhaps in /.config/gtk-3.0 or in /.config/gnome-shell...
You can take a look before restoring /.config-bkp and see if that fixes things.
If this does not work, check in /.local/share/gnome-shell and see if there is anything in there. If nothing, check if /.local/share/themes exists and if it contains anything.
