My 941 report from Full Service Payroll plan shows zero employees instead of 6

The 941 employee count includes only employees that were paid during a payroll period that includes the 12th of the third month of the quarter.  So, is it possible that you did not have a payrun that included June 12th?

Welcome to the Community, bookkeeping20.
 

When generating 941 reports, QuickBooks Online pulls information from employees you've paid with a pay period that includes the date(s) of Marth 12 (Q1), June 12 (Q2), September 12 (Q3), or December 12 (Q4). You can run a Payroll Details report to confirm the number of employees who should be on your form.
 

Here's how:
1. In the left navigation bar, go to Reports.
2. Enter Payroll Details in your Find report by name search field.
3. Change the date range to a specific quarter.

4. Hit Run Report.
5. Review the pay period below each employee's name.

If the number of employees listed in your form is still incorrect, I'd recommend contacting our Customer Care Team for assistance:
1. Click your Help (?) icon.
2. Select Contact Us.

Be sure to review our support hours so you'll know when representatives are available.
 

I've additionally included a helpful resource which goes into further detail about how 941s are generated: How QuickBooks Populates The 941
 

I'll be here to assist if there's any questions. Enjoy the rest of your day!