The reason for the new version isn’t entirely clear, but the original third developer beta was not available for the iPhone 7 and 7 Plus for some reason. Today’s update, build 17A5522g, is only a very minor increment from the 17A5522f build of the original release, but Apple appears to be pushing it out for all devices, not just the iPhone 7 and 7 Plus that had not originally received it.
Registered developers will need to download the profile for the iOS 13 and iPadOS betas from Apple’s Developer Center. The revised Beta 3 can be downloaded over-the-air once the proper profile has been installed.
https://www.macrumors.com/2019/07/08/revised-ios-13-developer-beta-3/