1. I bought it on the 1st of March
2. I've only used it on Switch and for the time I used it it worked flawlessly.
3. Yes, I've made a custom profile for Splatoon 2 and Mario Oddyssey
4. Nothing that I can think of, I took a break from Splatoon 2 for a week and when I decided to play it again with a friend it just wouldn't react to Mouse and Keyboard input, I decided to hook it up to the pc and check if maybe the profile's been wiped. That's when I got the error message and decided to look up the green light and 4 beeps on the forums.
I've used another USB cable for the video, mainly because I was trying out several cables and that happened to be the one I was using while recording the video. In total I've tried 4 cables now and 3 Computers, all giving me the same result so that I can conclude that it is not a failure of the USB-Cable or PC.