When an application has a very long package name, the debugger fails to start with this message:
Couldn't connect to logcat, GetProcessId returned: 0
The reason why this happens is not clear.
Thank you for taking the time to submit the bug. We are unable to reproduce this issue (Visual Studio for Mac will not let me create a project with a very long project name). Please attach a reproduction to the bug by starting with a clean Xamarin.Android project and adding just the code necessary to demonstrate the issue.
Found another bug that already details this issue, along with some more details.
*** This bug has been marked as a duplicate of bug 44420 ***