Quote Line Groups are not present on Amendment or Renewal Quotes in Salesforce CPQ

This is expected behavior in Salesforce CPQ. Edit the renewal or amendment quote and recreate Quote Line Groups as needed. Custom automation such as triggers can be used to help retain and populate the same group information from the original quote. 

Note: If Quote Line Groups are present on a Quote, 'Group Line Items' (SBQQ__LineItemsGrouped__c) on the quote needs to be true. If Line Items Grouped is true on the quote, all quote line must belong to a group. Missing group data can result in the Quote Line Editor displaying an infinite loading behavior.