Seems to be reoccuring on almost all new installations. However, the only way to fix this is reinstall pureftpd or install CyberPanel without ftp.
Run this to remove pure-ftpd software package and reinstall it again just to eliminate any package and conf corruptions:
# create a snapshot of your server
# stop the service
systemctl stop pure-ftpd
# remove package and leftovers
sudo apt-get purge --auto-remove pure-ftpd
sudo apt install pure-ftpd -y
groupadd -g 2001 ftpgroup
useradd -u 2001 -s /bin/false -d /bin/null -c "pureftpd user" -g ftpgroup ftpuser
systemctl start pure-ftpd
mkdir /etc/ssl/private
openssl req -newkey rsa:1024 -new -nodes -x509 -days 3650 -subj "/C=US/ST=Denial/L=Springfield/O=Dis/CN=www.example.com" -keyout /etc/ssl/private/pure-ftpd.pem -out /etc/ssl/private/pure-ftpd.pem
rm -R /etc/pure-ftpd
mkdir /etc/pure-ftpd
cp /usr/local/CyberCP/install/pure-ftpd-one/* /etc/pure-ftpd/
systemctl restart pure-ftpd
If you get an error that Access denied for user ('cyberpanel' @ 'localhost' ... run the following command nano pureftpd-mysql.conf and change the password to correct cyberpanel user password you can find it here /usr/local/CyberCP/CyberCP/settings.py under DATABASES =