Hi Hugo,
I had a look at the configuration.

Setting default is working for me. I use the “experiences” as the slug while modifying the tab.

If it is not setting the default tab, the possible reasons could be:-

1. You might have more than 1 tab set as default landing tab in the entries. In that case the first one get the preference. I suggest checking for this.

2. Or you are using a plugin or code that sets default tab for a group.

Please check and let me know.

Regards
Brajesh