Hi,
I just began using Piwigo too, and had the same problem as you.  For me, I misunderstood the interrelationship between locked/unlocked and public/private.  The tutorial explains it well; but I missed it.  The two are independent: locked/unlocked is for Admin use; public/private determines who sees an album.  All this is complicated by multiple methods to assign view privileges.  Noting the details will likely solve your problem.