This thread has now been closed to direct all further updates about this release onto the new Stable release announcement:
This is a bugfix release to address a few breakages caused by OS X 10.11 El Capitan.
If you find any new issues in this release compared to the current Stable versions, please do file a quick bug report, and then feel free to add a note on this thread with the bug number. Thanks!
You can downgrade back to the current Stable version by switching updater channels.
Release Blog including estimated timeline to Stable: https://releases.xamarin.com/beta-release-ios-9-1-xcode-7-1-support-el-capitan-fixes/
[This section will be updated if any new issues are reported.]
The remaining known issues from older release threads ("Android M Support", "iOS 9 Support – Service Release 1", "Cycle 5 – Service Release 4", and earlier) are unchanged.
EDIT Oct 26: Update bug-filing links for more precise bookkeeping.