Help to debug why QRB5 crashed

[kitkatSG]

Last Friday, I flew the QRB5 outdoor with manual mode (2nd attempt outdoor after purchase). We set up a laptop as a Wi-Fi hotspot which allows QRB5 to connect to QGroundControl (QGC) for controlling the drone. Besides the QGroundControl, we have an RC controller (i.e., DX6e) for manual mode and emergency brake. But we face the following issues:

• Out of control drone: Increase throttle small but the drone flew very high, and decrease throttle small but the drone tried to land immediately. Even though we tried to increase the throttle right after the decreasing attitude, the drone did not respond to the command from RC. After it crashed into the ground, it flew again due to delayed commands of increasing throttle that had been received. In this flight log, we used Manual mode to control the QRB5 drone via RC controller. Can see the video here
• Intermittent connection between QRB5 and QGC via WiFi: the connection is OK if the drone was put nearby the Laptop (within 5m); however, the connection was lost (most of the time) when we moved the QRB5 further the laptop (around 10m).
• Cannot send a Mission fly paths via QGroundControl: We can set many modes available in QGroundControl (e.g., Manual, Stabilized, Attitude, Position, Takeff, Offboard). After defining a Fence (for safety fly zone) and a Mission, we uploaded successfully to the QRB5. But we could not activate the mission (the QGC alarmed there was a critical check not passed, but not clear what?).

Could you (e.g., tech team) help identify the issues and guide how to fix them? Thank you.