looking at the import warning and the XML, target references of several data input associations are undefined. I tried to reproduce this bug and realized that this happens when a task is connected to a data object, and the task type is changed afterwards (for example to a user task). This causes the import warning.
I created a bug ticket for that: https://github.com/bpmn-io/bpmn-js/issues/694
What you could do until the bug is fixed: delete and reconnect all data input associations between tasks and data objects and you should not get the warning.
Thanks for reporting that bug!