Why does Site Contents page show in classic experience on modern site???

[Ingeborg Hawighorst]

Hello,

I just used the NEW admin centre to create a new site collection with the option to have no connection to an Office 365 group. The home page is modern. The document library is modern. But when I open the Site contents page, it shows in classic experience, with the big tiles for lists and libraries. 

WHY???

And how can I change that? In SharePoint Admin, the setting for List and Libraries to default to modern has disappeared. 

Where can I set ALL the pages of the site to modern experience?

[#2 · Accepted solution]

Sigh! It was Chrome's cookies. I found the page showed in Modern on a different computer. So I cleared Chrome's cookies for anything with "SharePoint" in the URL and that fixed it.