No automatic searching is not good for the network. If all gnutella programs did that it would slow everything down incredibly. Sometimes a file won't connect because the host has no free upload slots (busy), or they are simply difficult to connect to, or they have an unconfigured firewall system, or they have gone offline, or the files are fake. Best way is to re-search each one. This is best because people come & go offline all the time, so you can find fresh sources (hosts.)

BTW beware of fake files: Recognising fake files