Offline sync issues
Changes made offline aren't syncing back when you reconnect.
Steps
Check the connection. Open Settings, Offline Mode, Open Offline Settings. Connection Status must say Online. If it says Offline, fix the Wi-Fi or mobile data first.
Look at the counts. Pending Changes are waiting to be sent. Not Saved are changes the server refused.
Send them now. Press Sync Now. Waiting changes are sent oldest first. If your session has ended, sign in again and press Sync Now.
Read refused changes. Each change under Changes that could not be saved shows the server's reason, such as a time slot that was taken or a missing field. Enter the change again online if it is still needed, then press Discard.
Storage. Local Storage shows what is kept on this device. Browsers limit it. If it is full, press Sync Now first, then Clear Data.
Last resort: clear this device. Clear Data removes everything kept on this device, including changes not yet sent. Only do this after Sync Now, or when you have decided to abandon those changes.