In default.inv there is a section

[prometheus_hosts]
#localhost

This leads to Prometheus getting enabled on collectd (which starts a web service

There are 2 ways to fix this, the quick way is to comment out [prometheus_hosts] eg

#[prometheus_hosts]
#localhost

The correct way is to check if the list of [prometheus_hosts] is not empy, and enable the plugin if the list is not empty