Every time a new item is added to the list and the list is refreshed, the widget's update function is being called for every instance on the page. This is causing the multiple executions of the data source microflow.
This is the same behaviour you see using a standard dropdown (e.g. reference selector) in the list view with the data sourced from a microflow.
Not sure there is anything we can do to address this in the widget... looks like it is expected behaviour?
On change: The microflow that will be run when an item is checked or unchecked. Show Progress Bar: Whether to show a progress bar when executing the on change microflow. Progress Message: The message to show in the progress bar.