From Grosh 4, list syncing works a bit differently. In the past, it synced all the time, for even the smallest change on a list. In Grosh version 4, if modifications exist, they are batched together and sent to the server as a whole. The change significantly reduces network traffic and speeds up the app. The change also makes it possible to use the app when you are completely without network coverage, e.g. in an underground grocery store.
To sync the list, you just use pull-to-refresh (place finger on the list, move it down a bit, and release your finger) or press the refresh icon shown top right. If you don’t do so, the app will sync by itself the next time it is launched or by itself within 10 seconds (if modifications exist, requires Grosh 4.1.1 or newer). The same applies if you’re out shopping and marking stuff as purchased – again you should use the pull-to-refresh or wait for the auto-sync (Grosh 4.1.1 or newer) as this will not only save what you’re marked as bought, but also check if your spouse added anything to the list.