In both widget and app, when editing a task the labels previously added to task gets removed. The field "Labels" is empty, and as a non-premium user you're faced with a message saying "You have no labels. Upgrade to premium...".
But I did have labels, I added them using a web browser (and I could add them again by writing them in the Task field instead of the premium Label field). So editing existing tasks in the widget/app is quite useless today.
Thank you for your report, I've been able to reproduce this issue and I've passed it to the developers. Sorry for the inconvenience.