I worked only in the file explorer, connected to the sharepoint site associated to my Teams. I made changes on folders of both my 2 channels (add, rename, delete folders and documents). And I get the problem on the both.
I did not change authorizations. Sharepoint site and folders are still accessible from Sharepoint URL.
While clicking on the file tab, I got the picture attached in my first comment, it's indicating : "These files are no longer available" "Check the site avaibility, then retry". Plus the detailed message "Exception encountered from Sharepoint for requestId guid Scenario ID: xx"