Environments using Chrome's hardware acceleration feature sometimes experience missing shapes and lines in the editor and upon export. This is a known Chromium issue, and a bug report has been filed.
Meanwhile, please follow these steps:
- Navigate to "chrome://flags" in a chrome browser
- Disable 2D canvas hardware acceleration
- Clear cache: https://support.google.com/chrome/answer/95582?hl=en
- Restart your browser
Please email firstname.lastname@example.org if that does not resolve your issue.