Hi Jeff,
Yes, 100% certain. I got the email from Google about a day after uploading the brand new site and I have never received one before. Previous site had not been updated for 6 years (it wasn’t responsive in any way).
This was my mistake. The email notification didn’t tell me which pages were problematic… turns out it was an old html file that was on the server. Sorted the problem and it was nothing to do with Webflow.