Missing data when applying apromql calculation

[xkilian]

On Serveur2 with Prometheus 2.23 or 2.27.1

I run a query against a metric with a calculation (any will do that apply to a vector, like rate, avg_over_time, etc.) In he following example I use rate.

rate(ifHCInMulticastPkts{host="HOSTNAME",ifName="ha2"}[2m])

Rate should return a constant 0.5 every minute, but returns the following:

1624870560000, 0.5
1624870620000, 0.5
1624870680000, 0.5
1624870740000, null
1624870800000, null
1624870860000, null
1624870920000, 1.5037673189544352
1624870980000, 0.5

The raw data is present. If I collect the same data using another prometheus serveur running 2.27.1 on a different machine, the data is collected and displayed correctly both raw data and with a vector calculation.

This behaviour applies to all the metrics collected from the same device and other devices, but not all other devices.

• No errors in the logs
• Does not seem to be related to reloads or restarts
• Changing the step, time range doesnt change anything.
  

I am not sure what I should be looking at to troubleshoot.

Thank you for your help.

xkilian