Trezor Examples only work intermittenly

The example I'll be using is the 'TrezorV1PingExample' but others have the same behaviour.
Environment: Trezor v1.4.0, macOS Sierra

Sometimes the ping example works succesfully, other times it rejects one message and gets stuck in a loop afterwards, see the output in this gist:
https://gist.github.com/mrosseel/8065264579fe7418399b02346519d07c

Any idea what could cause this issue?