Solved

Selling drivers

For some reason the two last drivers I tried to auction simply weren't bid. By anyone. I tried multiple auctions, with no difference. And they are very attractive drivers, talent 16. I think it's probably a bug.

What makes me think like that is that I had to use the "sell now" option with this driver: 
https://igpmanager.com/app/d=driver&id=5060934
As no one had placed a bid in the multiple times I tried to auction him. That happened over a month ago, and the "buy now" option costing 3 tokens is still there, which I believe means he hasn't gone to the transfers market yet.

Not every single driver gets sold in the transfer market. Some are just not what buyers are looking for maybe the spec or even the salaries of the drivers. But this is normal and not a bug.