Please see https://releases.xamarin.com/service-release-cycle-9 for the details about this release, including the steps to update or downgrade as needed.
For Visual Studio 2017 users, the next available Xamarin update in the Visual Studio Installer will combine the fixes from this service release with the features from the current Alpha feature preview. Watch for more news on that update over the course of this week.
Among the fixes as mentioned in the release notes, this release includes fixes for the top visibility issues from Cycle 9 (specifically, bug reports from the "Cycle 9" list that had at least 3 users on CC as of March 6):
[Xamarin.VS] – 52760 – Breakpoints non-functional and exception call stacks show user code as "External Code" for PCLs referenced by PCLs on both Android and iOS
[Xamarin.VS] – 52695 – VS 2015 now hangs when opening solution that contains a Xamarin.Android project
[Xamarin.Android] – 52845 – Satellite assemblies not bundled when using "Bundle assemblies into native code" due to "unknown escape sequence" error from gcc during mkbundle step
The latest pre-release versions of the Xamarin.Forms NuGet package (version 2.3.4-pre3 or higher) contain a fix for the 1 other top visibility bug from the list (as of March 6):
(Note that the bug IDs in this query include some non-public bugs.)
Please file a quick bug report using the "Cycle 9" new bug form if you see any suspicious behavior in these versions that you wish to report.
You can also check the list of remaining issues reported by users so far for the Cycle 9 Stable channel versions to see if any match. If you find a match, feel free to CC yourself on the bug report as a way to tally your interest in the bug:
(If you have reported an issue that is specific to the latest Cycle 9 versions but is not yet included in the list, the bug might not have been filed using the "Cycle 9" new bug form. Those bugs will be added to the Cycle 9 list as they are reviewed by the team.)
Comment in this forum thread if your question is not related to a suspicious behavior after download, but instead one of the following: