Hi
We found that duplicating a page seems to generate 3 thumbnail.yml files in the Web-Files folder. This is using the functionality provided in the Designer - Select the page -> 3 dots -> Duplicate. The files are all identical apart from the the webfileid and they all reference thumbnail.css as the adx_name. We can't see this file, but it's referenced in the <head> of the home page:

We deleted all 3 files and now the line above in yellow has gone.
This seems to be a bug with the duplicate page option. If so, where would we report it?