Use this to reproduce:
<u-tabs>
<u-tablist>
<u-tab>Tab 1</u-tab>
<u-tab>Tab 2</u-tab>
</u-tablist>
<u-tabpanel><button>123</button>Panel 1 with <a href="#">link</a></u-tabpanel>
<u-tabpanel>Panel 2 with <a href="#">link</a></u-tabpanel>
</u-tabs>
<style>
/* Styling just for example: */
u-tab { padding: .5em }
u-tab[aria-selected="true"] { border-bottom: 4px solid }
u-tabpanel { padding: 1em; border: 1px solid }
</style>
When you tab inside the first tab, the button gets focus. On the second one, the panel gets focus before the link