There are some answers on SOF but in my case this was caused by no more disk space.
Checked permissions and they had the web server user www-data with write access to all app/tmp/*
Checked the /var/log/apache2/error.log and found a “no space left on the device warning”
Therefore did a disk clean up and suddenly started working again
https://www.bleepingcomputer.com/forums/t/642063/keep-seeing-something-hosted-on-port-9009/?p=4202486 Turns out is a...