in both cases (my application and the fresh Centurion install), I added 2 published pages under "Frontoffice"
"Frontoffice" node is at top level in navigation tree
found it: I deleted "anonymous" user in my application, adding it back solves the problem
thought it was a test back office user
IMHO, this is strange
for me, users are back office users, why require it to dsplay front office navigation?
anyway, thanks for your help