A session is missing from the app

In almost every case the session is still safely on the sensor and simply has not transferred yet. Work through these in order.

1. Was it actually recording?

The light blinks red during a recording. If it was off or blue the whole time you were on the water, the session never started. This is the most common cause by a wide margin.

Recordings shorter than about five minutes are not kept either. If you only rode for a few minutes, there is nothing to sync.

2. Put it in sync mode and open the app

Short press the button until the light pulses blue, put the sensor next to your phone, open the app and tap SYNC. Leave the app in the foreground until the transfer finishes. Transfers do not run reliably with the app backgrounded, because both iOS and Android throttle Bluetooth and network work for apps that are not on screen.

Your phone briefly joins the sensor's own Wi-Fi network to copy the session. If it says that network has "No Internet", stay connected: that is normal.

3. Check the battery

A sensor low enough to refuse to start cannot transfer either. Charge it for twenty minutes and try again.

4. Restart both sides

Force-close the app and reopen it. Shut the sensor down by holding the button until the light goes out, then switch it back on with a short press. Switching on starts a recording, so give it one more short press to get the light pulsing blue before you sync.