Known Issues - Windows 10 Mobile Insider Preview Build 14977
Known issues for Mobile
Please avoid attempting to install new languages, keyboards, and speech packs on your phone. There is a chance these downloads may get stuck and not finish downloading. If you have existing languages, keyboards, and speech packs installed – they will carry over when you update to new builds. You can use Windows Device Recovery Tool to go back to Windows Phone 8.1 or Windows 10 Mobile, install any languages, keyboards, and speech packs you need and then update to the latest build in the Fast ring as a workaround.
Windows 10 phones with 8GB of internal storage such as the Lumia 550 and 650 will likely receive an 0x800700b7 error when attempting to update to this build.
System related notification toasts (e.g. Bluetooth, USB/Autoplay, etc.) do not work.