This can happen when the device is an old-ish model (measured in Apple years, not human years), and it may be getting a little bogged down. This happens when a device has seen a bit of use and may not have been shutdown or cleaned up as often as it likes, resulting in a full life of data and history on board. The Cavanti app pushes a lot of data around and can be a bit of a resource hog, so is often the canary in the coal mine for these issues.
Some suggestions:
- Check for sufficient memory. When your storage is getting tight iOS spends all sorts of time shuffling stored data around to try and find space for the new data. It can end in freezes.
- Delete data, apps and photos you don't need or use.
- Restart your device. This will clear the data in memory.
- Check out this support article from Apple, it has some suggestions too.