I had a problem with the machine Observium is running on. The CPU fan/heatsink fell off. After I got the machine up again on the evening of 11 June, the CPU Temp graph showed normal temps in the 30-45 range for months, then a big spike up to 115. (eek!) But at least the server came back to life, and I still had all my data.
Everything still seems to be running OK, but all of a sudden there is now no data at all in the CPU temp graph before ~1:00AM 12 June. From this machine I get temp readings for CPU temp, Motherboard temp, and 4 other "temp#" listings. "Temp1" and "Temp3" still seem to have the data they should, but the others are missing.
One thing I did change after the recovery: I noticed the time zone on the server was set to US Eastern, and I changed it to US Central. I would think if that was the cause of my problem it would hit a lot more of the data.