weird formatting on USB, after interaction with Serato DJ?

So I am using my USB stick for storing music and playing with Serato DJ - not sure if the software is related to the issue or not.

Basically, I imported my library within Serato DJ.. today I was goa play and noticed, that the whole folder with music is missing. This is what it looks like.

I can't open the files.. nothing. I've never seen something like this and I am quite shocked, as it had 300+ songs... which I didn't have backed up unfortunately.

Is there a way to restore the original files ? Why did something like this happen ?