Feedback
You can send Feedback directly to Google, from your site, to report bugs and make feature requests:
Open your Google Site in the editor.
Use the three-dot More button towards the top right.
Choose 'Help Sites to Improve'
Enter your description of the feedback
If you wish you can send a screenshot to highlight the important points - be sure to blackout any personal information.
Use the Send button
If you want to watch a video on how to accomplish the above see Steegle's video https://www.steegle.com/google-sites/how-to/send-feedback.
Google does not respond to the feedback you send. Google say they use it to see the issues and feature requests users report and then can potentially act on them in the future.
You can review feedback you have sent at https://www.google.com/tools/feedback/reports
https://support.google.com/sites/community-guide/242187070