RRD4J recording wrong values

Add-ons Persistence Services
1

I mentioned this in another topic related to getting RRD4J, but thought I’d create a new thread for the issue.

I have an ESP8266 with two temperature probes connected, using the same code to read the value from each DS18b20. The value is then published over MQTT, which I can view in my Android client and on my OH sitemap as such:

However, the fishtank temperature logs fine, but the livingroom temperature is erratic when logged on a chart:

In my config both items are configured the same as far as I can tell.

rrd4j.persist

$
Strategies {
    // for rrd charts, we need a cron strategy
    everyMinute : "0 * * * * ?"
    everyHour   : "0 0 * * * ?"
    everyDay    : "0 0 0 * * ?"
    default = everyChange
}

Items {
    // which data to be stored
    Temperature_Sensors* : strategy = everyMinute, restoreOnStartup
    Bathroom_Humid : strategy = everyMinute, restoreOnStartup
}

Items

Number Fish_Tank_Temp "Fish Tank Temperature [%.1f °C]" <temperature> (Temperature_Sensors) {mqtt="<[oh2:hab/livingroom/temperature/0:state:default]"}
Number Living_Room_Temp "Living Room Temperature [%.1f °C]" <temperature> (Temperature_Sensors) {mqtt="<[oh2:hab/livingroom/temperature/1:state:default]"}

Has anybody seen rrd4j record such odd figures before or know what could cause it?