Your test suite might be too slow
The default timeout is an hour. Does your build regularly take longer than that? Then add a rule like this to your bors.toml file:
# Set bors's timeout to 4 hours
# https://ddg.gg/?q=4+hours+in+seconds
timeout-sec = 14400
If you don't have a bors.toml file, you'll also need to manually write out the CI systems it listens to. When no file is present, bors will try to guess, but if there is a file then you need to manually specify everything. For example:
status = [
  "continuous-integration/travis-ci/push",
  "continuous-integration/appveyor/branch",
  "ci/circleci",
  "continuous-integration/codeship",
]
Your CI system might not be building
Make sure that your CI system is configured for building the staging branch:
Your CI system might have an excessive backlog
Check in your CI's dashboard to make sure it doesn't have nineteen builds backlogging everything.

