Just overlap what graphs you can or copy and paste them to review side by side. As mentioned above you can look at temp probe, heater power, logging, level sensor or sensor, and see if they all align.
Difficult to tell with the graphs because we don't know the timeline of it. Just look at them all, overlay what you can, and you will know if it is something that actually happened or an anomaly. If it was low your ATO should have kicked in and you would see that although I don't know how your system is setup.
This is just my opinion and experience when I saw my temperature drop. I just pulled the temp and heater watt graphs and saw the problem right away. Heater was not drawing any power so knew it was bad. Replaced and all back to normal.