Android N is out there and it seems like the latest version of Xamarin.Forms is not compatible with it.
Can confirm that the SearchBar does not display when using Xamarin.Forms 18.104.22.168 with Android Nougat.
Did some digging and it appears to be related to the Android issue: https://code.google.com/p/android/issues/detail?id=221304&q=reportedby%3DDeveloper%20-has%3Amergedinto%20type%3Adefect&colspec=ID%20Status%20Priority%20Owner%20Summary%20Stars%20Reporter%20Opened&start=500
You can work around this issue by giving your SearchBar an explicit HeightRequest value.
*** Bug 44171 has been marked as a duplicate of this bug. ***
This is a Google issue as linked above but I'll set to confirmed for now to keep track of the status of this.
Same problem here. Which would be the default HeightRequest?
@dpedrinha 42 on Android, probably.