One of those packages is HAProxy (proxy/load balancer) and both work together very nicely but...
I have installed pfSense with HAProxy several times, more than several in fact... and every time I did it, the configuration file generated using HAProxy web configurator (integrated with pfSense interface) was broken. First row in the table showing defined backends was empty - the configuration file itself had just variables but no values. The second entry was just fine... Obviously HAProxy refused to start.
Just so I remember next time what I did. Get shell on pfSense console or install file manager package and edit /usr/local/pkg/haproxy.inc to add the line highlighted below:
Not a rocket science, just shift() the first (empty) backend definition and let the script do the rest.
Manually fixing config file is pointless because new config is generated every time HAProxy (re)starts and the code above is used to generate it.