This issue appears to only affect FireFox. To replicate:
1. Within a fresh Gradebook, create 3 GB items.
2. Drag and drop to reorder. Everything works as expected.
3. Now, from the center item, select the item's column header dropdown, and choose to "Move Left" or "Move Right"
Firefox will report a "The page isn't redirecting properly" error. Refreshing does not solve the issue. The URL in the browser contains the following after the tool id: