Excel tab in channel stopped working - file deleted or moved?

Hey all,

Certain Excel tabs in channels suddenly stopped working - displays the message "Sorry, this file has been deleted or moved. However, if I "Open in SharePoint" or in Excel from the "..." it opens fine. 

If i try to add this tab again, it just displays the same message, even though I navigate to the file and found it... What gives?? It was working fine.

PS: these excel files are being added from a Sharepoint folder - I added to the channel using the "Add cloud storage" feature. When did this stop working?