Screen has gone black and nothing seems to change it. Seems to be working but with a black screen.

I have the same issue, albeit I'm not sure it is recording (the only way I can tell it is switched on is button noises). Version 5.50.0.0. No amount of re-starting the various ways solves this. 

Unless you do not mean that it went completely black and you can’t see anything on your device you should check that you have not altered the display setting to be in night mode. There are 3 modes: auto, night, and day. Auto will change background color between night and day automatically depending on time of day. Night will have a black background with white text, and day will have the “normal” background. See the manual or do some exploring on your device to find the setting.

For my issue, the screen is completely black. Not even remotely an issue to do with display settings! NOTHING displays on the device as it is black / blank, therefore it is impossible to explore the device. Ticket logged.

I've had mine for about 2 months. Have an edge 520 that I've never had issues with so have reverted to this in the meantime! I have logged a ticket with Garmin so will see what they say next:) (I have no idea how long this process takes)

Logged ticket five days ago and heard nothing. They call this support.

Any idea on how long they take?

In my experience, 1 to 3 working days. For faster support, you can try chat or call.