Shared menu missing from finder sidebar
After upgrading to High Sierra, I had the same issue, coupled with SMB hanging without connecting to remote servers.

The SMB issue was solved by changing the SMB version to v2 in the /etc/nsmb.conf configuration file and rebooting the Mac as recommended in this post on SMB share deadlock. After the reboot with the new /etc/nsmb.conf, shared devices were again correctly listed in the sidebar, so I surmise both issues are linked.

The /etc/nsmb.conf file I use is:

$ cat /etc/nsmb.conf
streams=yes
soft=yes
signing_required=no
protocol_vers_map=2
file_ids_off=yes