Recording of WebSocket from Android App

Customer claims that he cannot record WebSocket message sent from their Android browser app. In contrast, he says he could record following scenario. Could you please, let me know what could be the differences? He tries to record with Proxy mode.

Scenario that works :
1. Open browser on Android and access https://websocket.org/echo.html
2. Establish and sent WebSocket messages with WS and WSS
3. NeoLoad can record both messages.

Scenario that does not work :
1. Open customer's browser App on Android.
2. He cannot establish WebSocket connection with NeoLoad.
3. He cannnot record WebSocket message

We only have an information like this. Sorry for the limited info but hope to get some clue.

Thanks!