Installing app from the "There's a new version..." notification email works fine on iPhone 5s but fails on iPhone 5c with error stating "Unable to Download App. App could not be downloaded at this time".
In App Center under the Distribution Groups > Devices tab the status column for both phones show as "provisioned".
Just want to ensure that App Center email installs should work for 32-bit devices such as the iPhone 5c.
Distribute should not have that constraint, it's most likely the way your application was built that probably does not have 32bits support, it should be a setting in your XCode project like armv7 in Build Settings Valid Architectures.