Not initialized with ActiveAdmin 1.1

[micleclickme]

ActiveAdmin uses jQuery3. So $(document).on('ready', function) is removed.
You should init with $(document).ready() call.
See https://github.com/activeadmin/activeadmin/blob/5ae2e3db5bf69e94ea8c205b83f04799154ceee3/app/assets/javascripts/active_admin/initializers/datepicker.es6#L14-L16 for example

[NechiK]

I have faced this problem as well. So you can use my fork https://github.com/NechiK/activeadmin-select2