Thank you, Lisa, thank you.
I was able to rest my own password through phpmyadmin. Thanks. I am quite sure other users, 600 at all, won’t be able to use that option.
Securi.net did not find any problem.
The site was probably hacked (through ftp?) because Wordfence deleted almost a thousand of suspicious files.
But the problem doesn’t go away.
If I try to type my own password, it gets replaced by an automatically generated password. WordPress generates automatic passwords and doesn’t let users choose their own passwords. I tried disabling all the plugins but unfortunately that didn’t help either.
Thank you/