Cannot add Order Fields to my checkout flow

I created my checkout field, and I added it to the Checkout display for the order.

I then went to /admin/commerce/config/checkout-flows/manage/default and drag/dropped the "Order fields: Checkout" item into the "Order Information" section. Then I clicked save.

When I got back into that Checkout Flow, the "Order fields: Checkout" are no longer in the "Order Information" section; it is now back down in the "Disabled" section. I am able to drag and drop any other item in the flow, except for "Order fields: Checkout".

Any ideas why this would be happening? I do see this error in Chrome dev console:

drupal.js?v=9.5.11:14 Uncaught TypeError: Cannot set properties of undefined (setting 'onDrop')
at Object.attach (commerce_checkout.admin.js?v=9.5.11:42:24)
at HTMLTableElement. (commerce_checkout.admin.js?v=9.5.11:22:37)
at Function.each (jquery.min.js?v=3.6.3:2:3003)
at E.fn.init.each (jquery.min.js?v=3.6.3:2:1481)
at Object.attach (commerce_checkout.admin.js?v=9.5.11:21:9)
at drupal.js?v=9.5.11:24:24
at Array.forEach ()
at Drupal.attachBehaviors (drupal.js?v=9.5.11:21:34)
at drupal.init.js?v=9.5.11:24:12
at HTMLDocument.listener (drupal.init.js?v=9.5.11:14:7)

I tried Claro and Seven admin themes; the issue occurs in both.

The issue does not occur in other drag-and-drop admin screens, such as managing the field display of a node type.

I am on Drupal 9.5.11. Planning on upgrading to D 10 very soon.