[Edit:] The following post talks about rrd4j database and not about InfluxDB. I should have read the question more closely.
IMHO this is no bug!
You have to understand how rrd4j works, especially how the archives work.
rrd4j uses archives to store the data, each archive is setup for a specific time (counting from now backwards). The first archive holds data for every time step (each Minute). All other archives do have larger steps, the value stored for that step is CALCULATED from the oberserved (minutewise) steps (for example MAX, MIN, AVERAGE, LAST)
When you request data from rrd4j, the database will look into that Archive that covers the requested timeframe.
Coming back to your example. You have a value of -7.2C observed during the last month, but you do not see a corresponding value when looking into the last 3 month.
Assuming you are using the Default Settings for the archives:
“AVERAGE,0.5,1,480:AVERAGE,0.5,4,360:AVERAGE,0.5,14,644:AVERAGE,0.5,60,720:AVERAGE,0.5,720,730:AVERAGE,0.5,10080,520”);
That way way the
1.archive has 480 values , each for a minute step (covering 480 minutes, i.e. 6 hrs)
2. archive has 360 values, each for a 4 minute step (covering 1440 minutes, i.e. a day)
3. archive has 644 values, each for a 14 minute step (covering 5040 minutes, i.e. 3.5 days)
4. archive has 720 values, each for a 60 minute step (covering 43200 minutes, i.e. 30 days)
5. archive has 730 values, each for a 720 minute step (covering 525600 minutes, i.e. 365 days)…
Looking into the last month, you got values from archive 4 (averages over 60 minutes), looking into the last 3 month you got values from the archive 5 (averages over 720 minutes).
Since all values are calculated from averages, a value seen in archive 4 migth not be oberserved in archive 5.
If you have REST Docs installed, you can display all values saved in the different archives (by using the correct requested timeframe).