Check if iCloud and iCloud Drive are enabled on all your devices and you are logged in with the same Apple ID into your iCloud account.See All my notes are gone for more details on this.
If your daily notes don’t seem to sync at all, check if you are using the same file extension on all devices and adjust the preferences if needed (under “Files”).If you are using CloudKit on other devices, they won't sync with this device. This can happen after a reinstall which wipes out locally saved preferences. If NotePlan can find files in your iCloud Drive, it will choose this method automatically.Make sure you are using the same sync method on all devices in the preferences under "sync": iCloud Drive or CloudKit.You can look up its status anytime on Apple's system status page. In very rare cases, iCloud might be slow or even inaccessible due to server issues.If you’re on a cellular network (3G, 4G, LTE, E), please verify that the options “Cellular Data”, “NotePlan” and “iCloud Drive” are activated in iOS Settings › “Cellular”.iCloud/CloudKit syncing is optimized for saving power and runs slower in Low Power Mode. If syncing is slow while you’re on a mobile device, try connecting to Wi-Fi and charging your device.Make sure you’re properly connected to the Internet.Fully reboot your Mac and iOS devices to make sure nothing is stuck in a temporary issue.If the sync is not working, please try the following checklist: 1. Dropbox is not working completely and not recommended to use. If you are using Dropbox, please change it to iCloud Drive or CloudKit. You can change it to iCloud Drive in the preferences. NotePlan 3 synchronizes your notes by default using CloudKit.