Hey there,
As Boubou mentioned, please make sure that you are posting in the correct forum for the game you are having issues with (this forum is specifically for Classic Games (Diablo II, Starcraft, etc). You can find the Diablo II Resurrected forum here
Just to add, the issue you’ve mentioned is known and appears to just be a display issue. Your mercenary should still have and use their original aura, even though it displays a different aura in their character window.
The Developers are aware and are working on getting the issue corrected.