I know this is an old question, but I just encountered a similar issue that Marketo support helped me resolve, so I'm posting the guidance here to help future wayward travelers...
Besides the Event needing to be within the 2 week window, the 'Event' channel itself needs to be properly configured. Specifically, your "Registered" or other default status must have a corresponding "Mobile Check-in Status" assigned to it. If this is set to "None," any events assigned to that channel will not show up in the app.
To configure this, go into Admin > Tags, and edit the Event channel. Change the 'Mobile Check-in Status' field next to your 'Registered' or default status, and save. Once done, your events should immediately begin appearing within the app.
Thanks Matthew this worked for me!!