There was similar issue back in 11.10/12.04 but I got that fixed some time ago so maybe unrelated to your issue with the SolusOs nautilus.
Post the contents of ~/.local/share/applications/mimeapps.list & these for some add. info, may be of interest, may not.
Code:
ls /usr/share/applications |grep nautilus
Code:
cat /etc/gnome/defaults.list |grep inode
edit: if you have a .desktop for nautilus in ~/.local/share/applications then also note that.