Just to add something on top of information available in the links above, I found the following.
Borrowers originating from Denmark are in oddly similar situations. For example:
Taking random loans form the list filtered by Denmark.
4 out of 5 borrowers are having about 1700 EUR of monthly income.
Minimum salary in Denmark around 17 000 DKK before taxes. This is around 2200 EUR. Not sure what to make of this.
Secondly, in the official UK register of Fast Invest there is another company originally registered in Denmark.
However, in the Denmark’s official register of companies, there is no sign of this company (it includes also the dissolved ones).
My takeaway is that I am discontinuing with investing in Fast Invest. For now at least. There are other companies (Mintos, Twino, Grupeer, Viventor, PeerBerry) which choose to be more transparent. I would recommend doing the same.