A bug in the Ryuk Ransomware encryption process could lead to data loss in large files. Ryuk was recently modified so that it does not encrypt the entire file if it is larger than 57,000,000 bytes or 54.4 megabytes. This is done to prevent the encryption process from taking too long, which could allow victims to more readily detect that the ransomware was running. The bug is causing the size of the file’s footer to not be properly calculated due to the variable nature of the encrypted block count.
Source: https://www.bleepingcomputer.com/news/security/ryuk-ransomware-decryptor-is-broken-could-lead-to-data-loss/