You can easily check what firmware version your Dash Cam currently has on the dash cam itself.

1) Turn the Dash Cam on
2) Stop it recording (by pressing the red square in the bottom left of the screen)
3) Go into Settings (the settings icon will show in the top left of the screen once a recording is stopped)
4) Go into Setup settings
5) Scroll across to ‘System Info’
6) Look at the Firmware number RXX.XX.

Then compare it to the Firmware number stated above. 

The minimum app requirements are Android 6 or iOS 13, and Bluetooth 4.2. Please check that your phone meets these minimum requirements.
Please check in your phone’s settings that all the app permissions are enabled for both the MyNextbase Connect and Alexa apps. These settings being wrongly configured account for the majority of app issues that users experience.
Please also ensure that Bluetooth and Wi-Fi are both enabled on your phone.
If you require any further help with an app issue, please contact Nextbase Support at support@nextbase.com, Live Chat or 02920 866429 (UK).

You have 'Dual Files' turned on in the Camera's settings. This means that for every recorded time period, two files will be produced; one HF and one LF- High Resolution Front and Low Resolution Front. If you also have a Rear Camera attached, then four recordings will be made; HF, LF, HR, and LR: High Resolution Rear and Low Resolution Rear. The smaller file size of the low quality video means it is quicker to transfer and edit within the app. Please note: Recording both high and low resolution versions will take up more space on the memory card. If you turn off Dual Files, then only the High Resolution footage will record.

You can disable Dual Files by:

1) Turn the Dash Cam on
2) Stop it recording (by pressing the red circle)
3) Go into Settings (the button in the top left)
4) Go into Video settings
5) Scroll across to ‘Dual Files'
6) Enable or Disable Dual files here.

https://cdn.nextbase.com/nextbase-en-gb/2019/03/522GW-Firmware-Update-Guide-Rev3.pdf

This is symptomatic of an SD card failure.

Please check that your card is not larger than 128GB and has a minimum U3 class.
Please remove the SD card, then press the reset button on the underside of the Dash Cam. Then, without the SD card inserted, please turn on the Camera. Does it now start normally? If so, then the SD card has either failed due to lack of formatting or is not compatible for Dash Cam usage.

If the Screen Saver is enabled on the camera, the camera's screen will turn off after 30 seconds of recording. The camera is still on and recording (indicated by the flashing red LED), it's just the screen that's been turned off (black). This is used by certain drivers to prevent distraction.

1) Turn the Dash Cam on
2) Stop it recording (by pressing the red circle)
3) Go into Settings (the button in the top left)
4) Go into Setup settings
5) Scroll across to ‘Screen Saver’
6) Enable/ disable the Screen Saver here

There's also a setting available called 'Speed Display'. This will allow the camera to act as above with Screen Saver, but instead of just a black screen, the vehicle's current speed will be displayed instead.

1) Turn the Dash Cam on
2) Stop it recording (by pressing the red circle)
3) Go into Settings (the button in the top left)
4) Go into Setup settings
5) Scroll across to ‘Screen Saver’
6) Select the Speed Display setting.
6) Enable the Speed Display here.