We’re hitting this problem on the AMP project.
While digging through the logs, I noticed that Travis jobs in multiple stages appear to be using the same merge commit (and same commit log) even though origin/master has moved forward. (I think this is what others are saying too.)
For details, see the comment at https://github.com/ampproject/amphtml/issues/21527#issuecomment-496717388
@acnagy, would it be possible to expose the commit SHA of origin/master at the start of the first stage of a Travis build via an environment variable, so that it can be used by subsequent stages to establish which files have changed by a pull request? I think this will serve as an acceptable workaround for us, instead of relying on the real origin/master, which is a moving target.