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I’m going to guess the reason might be that if you want to use binds like this, you also need to make sure that folders exists (check that it has a .gitkeep inside of it) Else it won’t exists and it doesn’t get created.
But I would rather suggest use a storage provider then bind the uploads mountPath etc.
From a docker perspective remember that each instance or when the server is empherial (I’m going to guess that Render gives a storage disk you can mount to it etc) but make sure the path then is correct and matching up with strapi etc.