Here's the list, as posted by Microsoft's Windows Insider head Gabriel Aul:
- Mobile hotspot doesn't work in this build. When sharing the Internet from your phone using Mobile Hotspot, devices will fail to get a valid IP address from your phone and will show no internet access.
- Two-factor authentication for your MSA with a phone number doesn't work in this build. If you reset your phone and go through the first run experience, you won't be able to input more than 2 characters for validating phone or text authentication. If you have a secondary email for two-factor authentication – you can choose that. As a workaround, add secondary email for two-factor authentication.
- Some phones might spend a long time in the post update migration experience – just let the phone sit and it should complete this migration.
- Apps that use background audio such as Groove, Podcast, Pandora, etc. will crash when launching after receiving an app update from the Store. Rebooting the device will resolve this issue.
- Some phones with a large number of tiles pinned to the Start screen may get stuck in a state where the device shows "Loading…"; the device will need to be reset or rolled back to Windows Phone 8.1 using Windows Phone Recovery Tool.
- Some apps may fail to update through the Store with the error code 0x80073cf9; uninstalling the application and reinstalling it will resolve this issue.
- The Movies & TV app will not work in this build (video playback is currently broken).