Chargify - Subscriptions are cancelled automatically in TEST mode

We have integrated Chargify in one of our web application for recurring subscription payments. Recently we observed that few of our test users, that are more than 6 months old, are unable to login in our staging site, which is connected to Chargify TEST Mode. We noticed that auto cancellations are happening (once a day) for these users in their Chargify subscription records. This was a strange behaviour. We thought either this is happening due to our Dunning settings in Chargify or due to unpaid state changes for credit card expiry. After debugging and verifying everything in our Chargify settings,