Files missing from new Sharepoint site collection

Hey, 

Can someone help understand this one? A solution would be wonderful since the importance of the content that was lost.

So, I created a new site collection (Team site) but by mistake I created one with a 365 group. So I deleted the 365 group and deleted the site.

I checked the URL and it gave me a 404. All good...

I recreated the site collection with a Teams site that does not have a 365 group. This went fine and the end user was able to work on the site and put some very important files on it.

In the admin center, I can see that the site was accessed and several files were on the site.

Over the weekend, something happened causing the end user to see a 404 message when accessing the site. I checked the site I created and it is empty. No files at all. The admin center still says there are files on the site.
The recycle bin stage 1 and 2 are empty.

 I have an idea of what happened,... but how can I recover the lost files?

Kind regards,

MVN