Hi, had the same error here, on multiple instances, multiple tenants.
Is now solved for what I see.
Message from Microsoft in the Admin Center:
Title: Errors when searching via quick find
User Impact: Users may receive an error when trying to search for a record using quick find.
More Info: When searching for a record via quick find, an error occurs: "A quick find filter cannot have any child filters". As a workaround, users may perform these actions:
1. Go to Settings > Customization > Customize the system
2. Locate the Account entity and click on Views
3. Look for the Quick search view for Accounts. It may appear as "Quick find view for active accounts". Double click to open it.
4. Click on "Edit filter criteria".
5. There's a filter to only search on active accounts. Delete the filter.
6. Save and close the view. Publish changes.
7. Refresh (Ctrl + F5) and try again.
Current Status: We identified a misconfigured setting preventing quick find from mapping correctly, causing an error when searching. We performed configuration changes on a test organization and restarted Internet Information Services (IIS), confirming that these steps mitigated the issue. We are currently performing the same steps to all affected customers.
Incident Start Time: Wednesday, November 21, 2018, 3:20 AM UTC
Next Update: Wednesday, November 21, 2018, 4:00 PM UTC