Diffing the raw logs (I use Winmerge) is useful to see what’s different.
I see that in Python 3.6 jobs, you are testing with a different Python version than your Travis config specifies.
That’s because in your
Pipfile.lock, there are modules that require Python 3.7 – I reckon you have last saved it from a later version of Python and some module has dropped support for 3.6 in its latest version. Due to this effect, since you’re testing with multiple Python versions, I suggest to delete
Pipfile.lock from version control.
Pipenv must be second-guessing you and choosing an appropriate Python version if it’s present in the VM.
That’s all I can say from the logs. To see what’s further up, need to see what Pipenv is doing while setting up its automatically-created virtual environment. I reckon you need to run
--verbose to see that.