When you perform "bulk action" on review items greater than 10k, the checkbox is disabled and greyed out and you will see warning "Too many items in this group to select all".
The product has a limit of 10k for groups hence the checkbox is disabled and greyed out and we show that warning in the tooltip.

As workaround to resolve the issue, use one of the options below:

Option #1: Perform bulk update i.e. maintain/revoke accordingly by ticking "Actions" checkbox and clicking 'Bulk Actions" button.
Option #2: Include more groupings and try to filter out so it will be <10k items and click 'Bulk Actions" button and bulk-update accordingly.
 

Follow the steps below for Option #1 to perform bulk update by ticking "Actions" checkbox and clicking 'Bulk Actions" button:

1. Tick the checkbox beside "Actions" on the upper left corner.
   
   
    

2. Deselect other checkboxes of groups which are not supposed to be actioned and then click "Bulk Actions" button.
   Upon clicking the "Bulk Actions" button, a "Bulk Actions" popup will appear.
   On the "Bulk Actions" popup, specify appropriate state (keep or revoke), then add comment and click "OK" button.
   
   
    

3. After performing the bulk update, save the bulk update by clicking on the "Save And Continue" or the "Save and Exit" button.
   
   
    

4. After saving the bulk update on the review items, the "Reviewed" progress bar is shown as 100% green.