Hi Zachary,
I'm sorry you are running into this issue. We have not yet been able to reproduce it on a High Sierra, however, we were only able to try it on one machine so far.
Can you please try the following
1. Completely remove Google Web Designer from your system by removing the app and running this command in Terminal to remove other files
rm -rf ~/Library/Application\ Support/Google/Web\ Designer ~/Library/Preferences/com.google.WebDesigner.plist
2. Reboot your machine.
3. Install Google Web Designer again.
4. Launch it and quit.
5. Run the following command in Terminal to disable gpu rendering:
defaults write com.google.WebDesigner.plist disable-gpu-rendering -bool true
6. Launch Google Web Designer.
7. Open a file, select Edit > Preferences > Advanced and turn on Verbose logging.
8. When you run into the issue again, quit Google Web Designer, then send us the log files in /Users/<username>/Library/Application Support/Google/Web Designer/logs
Thanks,
San
Google Web Designer team