title: Xamarin iOS and Android projects no longer compile
body: <p>This is for Xamarin 8.10.11 (Build 8) for MacOS, Community Edition.</p>
  <p>I recently returned to Xamarin development and opened a mobile project that I had worked on about a month ago.  However both the Xamarin.iOS and Xamarin.Android projects have a yellow warning triangle beside them saying that the appropriate tool chain is not installed.</p>
  <p><a href="https://i.stack.imgur.com/2cB4w.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/2cB4w.png" alt="Shows error bars" /></a></p>
  <p>Both are installed.</p>
  <p>If I download the latest DMG and request to install, it says there's nothing to be done (and indicates that both iOS and Android components are already installed).</p>
  <p>Any thoughts on what else I can try?</p>
  <p>The Show Details in the About dialog is missing all the relevant components (a colleague sent me their listing from a correctly working installation).</p>