Problem about collection-repeat and multiple view


I have an app with multiple tabs, and in the first has a list of item displayed with collection-repeat (display with flex box with 2 items every row). And this list is displayed at the bottom of the first tab. And I need to scroll down to show the list.

My problem is, when I open the app, and not scroll down, open the other tab directly. Then I go back to first tab, and scroll down, the items can not be displayed properly. It looks like the width of every item is 0.