I’m not raising this as a bug but as an observation as I’ve seen other people report it.
Quick backstory: I have a storage array that I have now attached to a local Yunohost instance and its file permissions need updating to use with my account, but I set up the instance and tried dropping files on the array using SFTP in KDE Dolphin and after a while, the connection was refused. Eventually, I thought to check the fail2ban log and spotted that my IP had been banned and noticed in the portal that the ssh log was logging ‘Permission denied’ because of a permission mismatch, and fail2ban was acting on that.
As the instance is internal I’ve ignored my home range with fail2ban-client set sshd addignoreip 192.168.x.x/24, but would suggest that if you get a problem like that, that’s one place to look.