Hello Constance,
Hope you're doing well.
Checking on your code, you have a mismatch between TabsHeaderItem widgets (4) and TabsContentItem widgets (3):
Usually, when you're using Navigation\Tabs, you should have the same number of TabsHeaderItem widgets and TabsContentItem widgets, so they can match with each other (a TabHeaderItem corresponds to a TabContentItem).
Another thing that I can see is that your TaskTable Block is only inside the Content placeholder for the first TabsContentItem. The others are empty, so it's normal that it doesn't appear when you change Tab.

In your scenario, the correct usage of this Pattern would be indeed to add a TabsContentItem widget (in order to match them with the Headers) and place your TaskTable Block (or the content that you pretend) inside of each of the TabsContentItem's Content placeholder:

Please refer to attached OML with these changes.
Hope that this helps you!
Kind regards,
Rui Barradas