So that is how they block a people's search/crawler. Didn't thought they would use the most complicated method.
They also use block lists to add every single TOR node (even if not an exit) and every VPN under the sun (except for streaming, because, why would them, that's why they exist)
After a year or two of hosting a Yacy instance (2014?) I started winding up on some general (probes, etc) blacklists.
I also host a small mail server and I was getting mail returned. I'd force an IP swap and a few weeks later it'd be the same. I had to let Yacy go.