If you think Grocery King app on your device is out of sync compared to the other devices in your sync group then there are 3 options you could try to get back in sync.
1. Firstly, go to "Account Settings" and tap on the "Sync Now" button at the bottom.
2. If that doesn't fix the issue, then you could tap on the menu button next to "Advanced Sync Settings" and select "Fetch all data from cloud"
3. If the above also does not fix the issue then it could be that the good data on your other device may not have pushed all data on the device to the cloud. You could open Grocery King on the other device and go to Account Settings -> Tap on menu button next to "Advanced Sync Settings" and select "Push all data on device to cloud". Once that completes go back to your device (one that hasn't synced) and try steps 1 or 2 to get back in sync.
Please note that syncing requires a decent data connection and if your cell phone data signal is low then you could try connecting to a wifi network and re-trying.