We are making some changes to the way 
qualityInfo and 
firstPageCpc fields are returned by 
AdGroupCriterionService in AdWords API. Currently, the 
qualityInfo and 
firstPageCpc fields are populated for 
BiddableAdGroupCriterion objects returned in response to 
AdGroupCriterionService.mutate API calls. Starting the week of June 15th, these fields will no longer be populated in mutate call responses. If you wish to retrieve QualityInfo or firstPageCpc for criteria, you need to retrieve them by making a 
get() call instead, using the appropriate 
selector fields. This change will affect all the active versions of the AdWords API.
If your code depends on the current behaviour of AdGroupCriterionService.mutate, please make sure you migrate your code by the week of June 15th. If you have any questions about these changes please reach out to us in the 
forum or during one of our 
office hours hangouts.
Update: We have extended the date for this migration till the week of 16th July.
 - Anash P. Oommen, AdWords API Team
 - Anash P. Oommen, AdWords API Team