I was using Bulk Read API to download all my modules as zip files. Until 24th May all the data was downloading correctly. But from 25th, all columns are not present in the downloaded zip files for most modules with lots of data. 

For example, 'Accounts' module in my account had 92 columns until 24th May. From 25th May onward the downloaded zip file of 'Accounts' module have only 49 columns. The number of rows remains same. 

Any idea what changed? I cant find any change in documentation.