Salesforce CPQ Error 'Cannot Read Property key of undefined' in Quote line Editor (QLE)

This error can appear when there is a quote line that has a value in the SBQQ__RequiredBy__c field that references a quote line from a different quote. This data mix-up is often a result of cloning records via a method other than the Salesforce CPQ package’s “Clone With Related” button available on the Quote object.

To assist in locating the quote lines containing the invalid data, please use the SOQL query below. If you plug in the Id of the quote that is experiencing the error in both places with <ID OF QUOTE WITH ERROR>, the query will return a list of Ids of quote lines on the quote with improper lookups populated in SBQQ__RequiredBy__c.
 

SELECT Id FROM SBQQ__QuoteLine__c WHERE SBQQ__Quote__c = '<ID OF QUOTE WITH ERROR>' AND SBQQ__RequiredBy__c != null AND SBQQ__RequiredBy__r.SBQQ__Quote__c != '<ID OF QUOTE WITH ERROR>'

Note: a Price Action injecting a null value into a Checkbox field (as opposed to a true or false) will also encounter this similar error: Cannot read properties of undefined (reading 'type') when adding a Product to a Quote. Review Price Actions that target checkbox fields and ensure they do not inject a null value to resolve the behavior.