Sudden errors on /tmp permission

One day ago all of a sudden I started getting errors like:

PermissionError: [Errno 1] Operation not permitted: ‘/tmp’

on a previously successful build. I diffed the raw logs and couldn’t find any significant difference and all my dependencies are controlled (cloned branches from our own forks). Is there anything I am missing? Here the full log:

https://travis-ci.org/intra2net/avocado-i2n/builds/509510502

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