This issue occurs when a locally created flow (or a flow created by process builder) in the subscriber org references the component in question. The dependency results in the following error:
Action NewEvent Component is in use by another component in your organization. myRule_1_A1
1. Review all locally created flows (including those created by process builder) in the org whose last modified time is later than the package installation installed date and time.
2. Remove any reference(s) to the component in question.
3. Attempt to uninstall the package again.
Note: If there are several flows in the org, you can retrieve all flows using workbench and download the ZIP file. Extract the file and use a text editor to search the component name being referenced within the folder.
In above example, a search for "NewEvent" should return the flow which has reference to it.
Package.xml file to retrieve flows:
<?xml version="1.0" encoding="UTF-8"?>
<Package xmlns="http://soap.sforce.com/2006/04/metadata">
<types>
<members>*</members>
<name>Flow</name>
</types>
<types>
<members>*</members>
<name>FlowDefinition</name>
</types>
<version>39.0</version>
</Package>
If there are any issues please open a new case with Salesforce Support.
See also
'Component is in use by another component in your organization' error
Best practices when you uninstall an app or package
Uninstallation of a managed package gives 'component type' errors
000384299

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