I have a power table set up to sample values in 24 hour intervals, but for some reason the daily sampling time keeps drifting by 30 minutes. So it is really sampling at around 24.5 hours. Any idea what causes this and how to fix it?
Have a look at the tips at the bottom of the docs, Configuring Tag History - Ignition User Manual 8.1 - Ignition Documentation. Use this to find out what's actually stored and start debugging from there. (You could create a custom property and create a dataset binding to it for inspection.)