First, you should use the default settings in CC unless it never works. These settings help handle IP addresses that change and add information to the logs.
As for what is happening: my guess is a congested network or an antivirus that decides from time to time that CC is evil. Another possibility is that some device is connected by cable to the computer running calibre, perhaps only for charging, and that device is preventing calibre from processing CC's connection attempts. This can happen even if calibre fails to connect to the device. Something similar can happen if you use calibre's connect-to-folder option.
I might be able to tell more if you provide debug logs. See
How do I get help? for instructions. We will need both a CC and a calibre debug log.