Rtl433/mqtt weatherstation problem

I’m running Home Assistant on a Odroid N2+ with RTL433 and MQTT to receive data from my Bresser 5-in-1 weatherstation.

This has been working fine for a long time, but yesterday it started showing strange behaviour, updating with hours inbetween, resulting in this:

For comparison, this is the graph Weathercloud is showing for the same sensor:

I’m showing only the temperature graph, but the same happens with the other weather station entities.

There have been no software updates directly before this behaviour started. What could be the cause of this behaviour?