Duplicate (empty) sensors reported for certain devices

Using 21.11.11767

I've been trying to figure out why I have '4 alerts' listed for statuses but clicking the alerts shows me nothing and I think I've got a lead - if I click 'statuses' and then inverse sort by event, I can see four sensors listed with no status or event (two devices, a powersupply and fan sensor for each).

If I look at the status indicators for each device, I cans ee the relevant statuses listed twice; one entry is OK, the other is blank. I tried re-discovering the device and watched the output and the duplicate blank status is shown there too. If I look at the graphs for the empy sensors it looks like they have previously logged some data.