If your partner has access to the same list you have and they are not in sync, then one of the phones is not syncing its contents with the Grosh servers. To figure out which one, please use our webapp by tapping Login in the menu at https://groshapp.com. The navigate to your list and figure out which phone is not syncing properly. Try uninstalling Grosh and reinstalling it on the device that is not working properly – this should solve your problem. If it does not then contact support at groshapp dot com.
