Luci-Statistics - Collectd or RDD Problem - Davidc502 Build r7093

I have a Luci Statistics problem.

It was working until mid-April (I just noticed it) and writing to a 64GB USB stick in a WRT3200ACM. I am using the latest Davidc502 build (Lede SNAPSHOT r7093-4fdc6ca31b / LuCI Master (git-18.152.60731-18b5b06).

USB stick is set for 777 permissions cascaded down through the complete directory structure.

I can read the old data by the graphs from before mid-April but no new data is being fed to the RDD files.

My set-up for the luci-statistics config file is below. Can anyone see any errors in the setup or provide some help to get it working again?

Do I need to post other configs to get to the problem?

config statistics 'collectd'
	option BaseDir '/var/run/collectd'
	option Include '/etc/collectd/conf.d'
	option PIDFile '/var/run/'
	option PluginDir '/usr/lib/collectd'
	option TypesDB '/usr/share/collectd/types.db'
	option Interval '30'
	option ReadThreads '2'

config statistics 'rrdtool'
	option default_timespan '1hour'
	option image_width '600'
	option image_path '/tmp/rrdimg'

config statistics 'collectd_rrdtool'
	option enable '1'
	option RRARows '100'
	option RRASingle '1'
	option RRATimespans '1hour 1day 1week 1month 1year'
	option DataDir '/mnt/sdb1/rrd'

config statistics 'collectd_csv'
	option enable '0'
	option StoreRates '0'
	option DataDir '/tmp'