Checks and branch protection
GitHub recently introduced the Checks API to allow integrations to report richer information against your commits. Unfortunately, they did so in a way that mixed up legacy commit statuses and the new checks in the branch protection API, leaving OAuth clients no way to disentangle the mess. The likely consequence for you is that if you have Travis CI set up Reviewable recently started showing bogus "missing" checks and refused to let you merge PRs.
I've implemented a heuristic that will allow Reviewable to ignore checks for now, and I'm working with GitHub support to find a better solution. Sorry!
Incidentally, I also fixed Reviewable's treatment of the "include administrators" branch protection flag so it should now be reflected correctly.