I went in my store setting to upload a new files but I cannot.
On top of the file page the link to upload is blurred and there is a mesage saying :
The uploaded files are being processed in the background
Solved! Go to the solution
This is an accepted solution.
Contact Shopify Support on this one. It feels like this is something they may to look closer at. There's not many posts by others talking about the same issue so is very unlikely to be widespread, but I did see just the one earlier today.