Same here on some situation…
Somehow the system “rounds up or down” the start time, making it miss even an entire hour…
Example:
Set “Last 3 hours” - it says “Last 3 hours”
Now press the “before” button, the one with “<” in front of the time interval.
It shows only the previous 2 hours and some, not 3 hours…
The same with 6 hours, 12 hours, etc.
Not to mention that the start of the interval is rounded.
Initial
Previous 2 hours and 5 minutes… NOT 3 hours.
It should be from 18:05, not from 19:00
The same further…
It should be from 15:05, not from 16:00
So the interval between 18:05 and 19:00 is never plotted in this situation… Almost an hour.
Or from 15:05 and 16:00…
And so on and so forth…
Seen it long before together with many others, but because of various reasons, lost the drive to report bugs…