Any new map that I create I cannot view, even when the permissions are set correctly, so the user is in the group with permission to see it. I can see existing apps just fine. I've done everything, even reinstalling Collector and wiping out the data and cache. So I'm guessing this is on the Portal side? What is blocking me from seeing those apps? Offline mode is enabled as well.
I found the problem. I only have one editable layer in the project and it mysteriously disappeared from the project after I enabled attachments on that layer and republished the service for it. I added it back in and now I can see the map which contains that layer in Collector again.