In https://travis-ci.org/github/native-api/test_travis/jobs/663728118, I accidentally read stdin with cat -n "${FF[@]}" when $FF happened to be empty.
It caused the build to hang (understandably), but output got truncated mid-line and long before the offending code.
(A sibling job in AMD64 environment, with exact same settings, correctly displayed all output up to the offending line.)
In another build with this defect, https://travis-ci.org/github/native-api/test_travis/jobs/663783018, the output got truncated at exactly the same place – which suggests that the output defect is connected to stream buffering.