Failed to get tickets message on Zendesk

We are using mobile sdk for android and iOS. Some of our users, (approx 1200+), are not able to view their tickets on our application. We checked everything on our side. And would like to know what could be the root cause. 

One test account that we have in a live environment is also facing the same issue. Email ID for that account is kunal@banknovo.com

We need urgent help in this matter. Thanks