Kasernet is designed to handle offline playback:

All downloadable content (pictures, videos, documents) will be downloaded to your device, so losing internet connection will not affect your playback.
When the device connected back to the internet, it will sync any changes, update made to the portal since it became offline.
Content that required live connection:

Such as Youtube, Vimeo, Social media content, will be interrupted if you don’t have an internet connection.
If you have a playlist that mixed downloadable contents and live contents, the live contents will be skipped over.
Changes made on the app.optisigns.com portal while the device is offline:

These changes will be cached, when the device comes online, it will receive the latest assignment and play the content as expected.