There are a lot of missing threads in User.threads.list ()

Question

I am retrieving threads from my GMail account using the Users.threads.list method with the request "in: sent newer_than: 1y". The first page of results (100 threads) looks fine, with threads from December 2014 and January 2015. However, the second page starts in June 2014 and returns in May 2014, etc. It seems that whole pages of streams are missing for the months of July-November 2014.

I reproduced this using the API tester at https://developers.google.com/gmail/api/v1/reference/users/threads/list .

Everything looks good in the GMail web interface.

I am sure it worked yesterday, that is, I was able to receive all the 2014 streams / emails.