[SalesForce] How to solve An unhandled fault has occurred in this flow (System.DmlException: Insert failed)

I am doing the trailhead and I am currently at the step: Apex Triggers Bulk

https://trailhead.salesforce.com/trails/force_com_dev_beginner/modules/apex_triggers/units/apex_triggers_bulk

Here is my code for this challenge: 

trigger ClosedOpportunityTrigger on Opportunity (before insert, before update) {
    List<Task> taskList = new List<Task>();
        for(Opportunity o : Trigger.new) {
            if(o.StageName == 'Closed Won') {
            Task task = new Task();
            task.Subject = 'Follow Up Test Task';
            task.WhatId = o.Id;
            taskList.add(task);
            }
        }
        insert taskList;
}

Here is the error message I received:

Challenge Not yet complete… here's what's wrong:
There was an unexpected error in your org which is preventing this assessment check from completing: System.DmlException: Insert failed. First exception on row 0; first error: CANNOT_EXECUTE_FLOW_TRIGGER, The record couldn’t be saved because it failed to trigger a flow. A flow trigger failed to execute the flow with version ID 3011r0000004rvE. Flow error messages: An unhandled fault has occurred in this flow
An unhandled fault has occurred while processing the flow. Please contact your system administrator for more information. Contact your administrator for help.: []

Here is the log I received:

https://docs.google.com/document/d/1kaaz3BB7qn8H_lepm4suATEdLkMaxu3cOHMyoIoHRok/

Best Answer

Pasting from comments:

Checked your log...Flow Closed_Won_Opportunities_Clone is causing the issue.

Deactivate it and try again. Also like I said as you are inserting other object records you should move your logic to after trigger.

Also Trailhead generally suggest to complete challenges in clean org and triggers, validation rules, flows etc need to be checked before submitting challenge as they generally cause some issues.

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