How often does the meter actually write to SD card:
Data is written to the SD card every 10 seconds. If you are logging with aggressive settings (like no time delay between samples) it might be written more often.
Proper procedure for removing the SD card:
Turning logging off before removing the SD card is technically the best way to do it, but the chances of corrupting a file are so low that I never do it myself (I just pull out the SD card). If you’ve been consistently seeing corrupt files, can I ask what kind of SD card you’re using? I’ve seen that behavior a few times from no-name brands, but generally quite rarely.
This is the on-chip temperature for the ADC (an ADS1292 if you are interested), and you’re right that it’s not extremely accurate for absolute temperature. So the readings you’re seeing are not abnormal.
Let me know how else I can help, best