A month after the arrival of its last Windows 10 Mobile Insider Preview, build 10166, Microsoft today rolled out a new preview release, promising big improvements in overall quality. Build 10512 is rolling out now to Windows Insiders on the Fast ring - but as you've probably already worked out, it comes with a few known issues.

Some of these issues are quite significant - for example, the Movies & TV app doesn't work at all in this build due to video playback faults. There are various other problems and issues to be on the lookout for, which Microsoft detailed in its release notes for build 10512:

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).

Given that this is still a preview release, it's a pretty safe bet that that's not an exhaustive list of issues with the new build - as with any pre-launch software, expect to encounter other undocumented bugs and crashes. If you're not prepared to deal with this, you should avoid installing the build on your phone - especially if it's your only handset.

Microsoft also mentions that the Insider Hub isn't included in build 10512, but it plans to reintroduce it in a future release.