I am having this issue on at least two different sites, one running v 2.1.0 and the other v 2.1.1. In both cases the file permissions are being set to 640 on uploaded images, on a completely random basis. I can upload loads of images with no problem, then for no apparent reason one of them ends up not displaying on the website (but OK in file manager and in the Channel Edit page). I check file permissions and sure enough it is set to 640 - I manually set it to 644 and all is fine.
This happens when uploading files using a file type field or manually inserting an image file in one of the Channel text fields.
Is this a known bug?