Updating to version 16.10.0 fixed this issue.
Although it introduced a different issue, "MessagingRemoteException: An error occurred on client Build1610000228 while executing a reply for topic xvs/build/execute-task/#projectname/dcef6ea002fACTool
IOException: Sharing violation on path /#pathto/Library/Caches/Xamarin/mtbs/builds/#projectname/dcef6ea8f073d59dc1c36cb1f5a222f318d7bca40b05591396d2da9756e6eedb/Assets.xcassets/AppIcon.appiconset/Contents.json"
Uninstalling VS 16.10.0 and reinstalling 16.9.6 fixed the "new" issue.
Maybe this is the universe telling me to learn Swift and Xcode.