Sometimes the automatic iCloud sync does not work, and new tasks don't appear on your other devices. Unfortunately, I don't have much control over the system, as iCloud is provided and managed by Apple. Nevertheless, there are a couple of things you can try to get it working. Make sure to check these steps on all your devices.
Check the iCloud Sync Status
Firstly, open the in-app Settings, by tapping the ⚙️ in the top-right corner, and then select the iCloud Sync entry. This will open a page with the current syncing status at the top. Usually, this should say Syncing... or Fully Synced, meaning that the sync is currently in progress (then just wait) or is already up-to-date. If this is not the case, check out the troubleshooting tips below.
Check the internet connection
iCloud sync requires a working internet connection to work. If the status is displaying No internet connection or some other error, make sure you are connected to the internet. Maybe check if some websites are actually loading.
Check if iCloud is enabled
If the status page is displaying Not logged into iCloud, then you'll need to check your iCloud settings. Go into the Settings app and make sure your account appears at the very top. Now tap your account and then iCloud. Check that iCloud Drive and Structured are enabled.
Check if you have enough iCloud storage
If the iCloud sync is still not working, make sure you have enough iCloud storage left in your account. Structured won't take up much space in your iCloud, but needs some to work. If your iCloud is full, check your iCloud storage plan or try to delete some stuff you no longer need.
If it is still not working?
Sometimes the iCloud sync is still not working, even after following all these steps. If that is the case, you could try to turn off Structured in the iCloud settings and then back on or reinstall the app. Keep in mind, that this may delete all your tasks. You won't be able to restore them.