Hello All,
The issue you are having with shipping is fixed in the sellacious 1.6.0-alpha. To fix this issue, please update your sellacious. And before the update, please take a backup of your site.
This demo link for 1.6.0-alpha
https://demo.sellacious.com/160-alpha/
Please take a look. As for now in sellacious 1.5.3 you can use flat shipping.
I hope this helps.
Thank You
-Team Sellacious