GPG failed to sign the data fatal: failed to write commit object` error occurs when Git is unable to verify a user's GPG signature, typically due to an expired or invalid GPG key. To resolve this issue, users can try running `GIT_TRACE=1` command to understand what's happening and then manually execute the failing command with their GPG key to diagnose the problem. Sometimes, the solution involves verifying that the secret key is properly set for the user in Git. On MacOS, users may need to uninstall and reinstall GPG, install Pinentry, generate a new key, and configure Git settings to resolve the issue. Additionally, using Jam's free bug reporting browser extension can help speed up debugging by auto-including necessary debug data and making it easy to create comprehensive bug reports.