same trouble for me after update omv3 to omv4 last week end, i solved it by replace collectd.conf in /etc/collectd/ by the new version of conf file and do (i have seen dpkg reconfigure error during update for this packet)
rm -r /var/lib/rrdcached/db/localhost
rm /var/lib/rrdcached/journal/*
service collectd restart
service rrdcached restart
make sure you have no error when u launch service collectd status
my conf file
root@NAS:/etc/collectd# cat collectd.conf
PIDFile "/var/run/collectd.pid"
Hostname "localhost"
FQDNLookup true
<Include "/etc/collectd/collectd.conf.d">
Filter "*.conf"
</Include>