I'm also experience this bug, and when the update is downloaded, it can't be installed. After I close Paint.Net as the "update-manager" says, and the installation begins, it says that it doesn't have permission to the file (C:\Program Files\Paint.Net\Staging\PaintDotNet_107149113.msi).
I realised that when I installed the Alpha (1), I installed it in C:\Program Files\Paint.NET Alpha\ (in the hope, that I could use both 3.10 and the alpha). Unfortunately, nothing was installed in that folder, but Alpha 1 downloads the update in it, and forgets that it isn't placed in the app-folder C:\Program Files\Paint.Net
After I click "okay" to the "update-installation-file-not-found", Paint.Net says that it has detected that some important installation files are missing, and wants to repair FileTypes\DdsFileType.dll. :?
