There is an issue in Magento 2.1.x that when you configure a minimum order amount, you can not delete all the items on the cart or add new ones if the total purchase amount is less than the minimum. Does your Minimum Order Amount For Customer Group For Magento 2 extension have the same problem?
Our module does fix the issue with magento default and works properly.
Could you please test out its function on our demo site?
For more information about product, please refer Minimum Order Amount For Customer Group For Magento 2 page.
If you need any further assistance, please feel free to contact us.
Please visit our site for more useful Magento 2 Extensions: https://bsscommerce.com/magento-2-extensions.html