Not sure that I have fully understood your issue. Did you mean that the data source of the gallery if Wunderlist, and after you add some items it won't update in gallery? Have you tried the Refresh function and the refresh button beside the data source name?
This is still an issue, When you try and add a task to the app it doesn't load unless you go on a different list and go back. I have tried the Update List expression and that didn't work, so now I am using this formula for the refresh however this doesn't work either
These expresssions I have been attempting are on the refresh button
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