https://docs.travis-ci.com/user/customizing-the-build#Git-Clone-Depth notes
Please note that if you use a depth of 1 and have a queue of jobs, Travis CI won’t build commits that are in the queue when you push a new commit.
I find this behaviour rather inscrutable... is depth 2 enough to make the queue work? Or do you need depth n where n is the number of jobs in the queue?