Hmm .... no that should not be the case i think ....
i am trying to reproduce but no luck so far.
on your x-axis, when you set interval to minute, do you get exclamation mark next to the selection saying you will get too many buckets ?
you are looking at last 30 days of your data ..... per minute interval just wont be possible (it would generate 55000 buckets .... too much to actually plot)
what if you select daily interval ? what if you change your metrics to count for example ?
looking at your screenshot, I don't see it divided by 10 ? for example on jan 5th at 12:00 you have SMS Success Count at 20,271 .... and in the chart it seems to be less than 100 .... ?