I did some testing using Set List Maker and BandHelper on a wi-fi network that has no Internet connection. What I found is that whenever the apps try to sync, that process will run in the background for five minutes, but then the final check to determine that there's no connection doesn't run in the background and freezes the app for between 10 and 30 seconds.
The apps sync whenever you open them or save any data in them. So I'm guessing what's happening is that some of you open the app and start to use it, and then five minutes later the problem occurs, and it seems random because the action that triggered it occurred five minutes ago. If you are switching between apps, the problem would recur whenever you switch back to these apps, with the same five minute delay.
I just updated my working copy so that the network check at the end of the sync process also runs in the background. After changing this, the sync icon will blink for about 5 1/2 minutes, but won't affect the app otherwise. The interface remains active, and audio playback and auto-scrolling are unaffected.
This change will be available in the next update. This change will only affect devices running iOS 8, because I haven't had success using background processes on older iOS versions. Also, this will only solve problems caused by syncing on a disconnected wi-fi network. Some people have said that the problem still occurs with auto-sync turned off, or is caused a particular app running in the background, but if you think this is the case, I'd encourage you to look more closely and see if database syncing is really what is triggering the problem. That's the only function in the app that uses an Internet connection.