Our theme does not have any compatibility issues with default WP editor. As a rule, everything depends on your server (timeout, file permissions) and on changes that you do in files. If you make any error WP won’t save your file and we faced the situations when WP just remove all the content from the file if any error was made and WP moves back the changes. And it was not just with our theme.
That’s why WP editor is not a good tool for development. Use FTP to implement new features.
