Steps to reproduce:

navigate to Content => tags and create two new tags named foo and bar below the taxonomy Root tag

Click on the Root tag, and go to its detail view tab, then scroll down to the 
Sub-item sorting order block
Try to change the order by content name or whatever, it does not work
The tags keep the same order
 
Expected result:
the tag sub items should be ordered according tho the selected options in the Sub-item sorting order block

NB:

The tags can be ordered by drag and drop, please share this with PM if either this functionality is not relevant for Tags tabs