Would love to see your code snippet but still there is alot yet morderate changes to ue5. So it can be how you are getting you box. Not giving error just mean you code is good in syntxt but logic is your.
If you are adding x and y mouse value to your box transform i do that then might be sign mistake. Or mouse location transform are not been send. just test one bit at time first get mouse then make simple text change on location then ad it to box. Also when you get old position for before been drage make sure that is not over wrighting the new position. Dont know your code so explain mine. Everybody have his/her style so pleace do sare snippets.