I found the root of the continuing MobileMiner issues and have updated to fix that as well as added some sanity checks in hope of fixing the mysterious and elusive crashing bug some users are experiencing on second app launch.
With 1.5.20b2 I see this error in system log (e-mail address and API key obscured):
08/05/14 16:19:35,357 MacMiner[72481]: Error getting https://api.mobileminerapp.com/api/RemoteCommands?emailAddress=xxx@xxx.xxx&applicationKey=xxxx-xxxx-xxxx&apiKey=26efrOXrizmEF3, HTTP status code 404
The RemoteCommands endpoint should also be passed a MachineName on the QueryString:
{Root URL}/RemoteCommands?emailAddress={Email Address}&applicationKey={Application Key}&machineName={Machine Name}&apiKey={API Key}