Search for "reproduce_ionic_cli_bug_2247" here:
https://github.com/realfreebird/reproduce-ionic-cli-bug-2247/commit/d0da52655a701ad004fcf11a44761fe01d65c70e
The problem is related to watching non-existing files.
Just comment out the following code, and everything works just fine.
reproduce_ionic_cli_bug_2247: {
src: ['{{ROOT}}/node_modules/non_exiting_file.txt'],
dest: '{{BUILD}}'
}