A number of users have been complaining of broken energy history data in the Nest app over the weekend. The thermostats themselves seem to be fine, but the app data is incomplete, which sounds like a real pain in the posterior. Thankfully, Google is aware of the issue and is currently working to fix it.
The problems have been documented by users on Reddit (via 9to5Google). It's likely connected to partial outages faced by the Nest network over the last few days, as outlined on the official support page. Energy history should show up eventually, but you may be noticing a considerable delay. Google says it's identified the cause of the issue and is on the case, so we can only hope that the resolution will be swift.
Google is slowly but surely migrating features from the Nest app to the Google Home app, which not everyone is happy about but it may lead to a better user experience eventually. As things stand, the mixture of features across both apps is more than a little confusing, so it's about time Google sorted it out.