The fourth version of pi-hole worked great.
After upgrading to the fifth version, it stopped blocking anything at all.
The network configuration has not changed. DNS requests definitely go through pi-hole, but it can resolve domains from the blacklist as if they are not there...
For example: r.mradx.net
# nslookup r.mradx.net
Server: 192.168.1.33
Address 1: 192.168.1.33 pi
Name: r.mradx.net
Address 1: 2a00:1148:db00::28 r.mradx.net
Address 2: 217.69.139.244 r.mradx.net
As you can see, the domain is on the block list, but pi -hole resolves it.
192.168.1.33 is the RaspberryPi address with the pi-hole installed in it.
The same thing happens with manually added domains to the blacklist.
I already completely removed the pi-hole and reinstalled the fifth version - this did not help.