I'm having the same problem. I tried the process described above, but it didn't work.

I used to be able to rearrange lines on invoices or journal entries by dragging them, but it stopped working most of the time.  It's very strange, it stopped working and then worked one time for a JE and the immediately stopped again.  I've cleared my cache, rebooted, tried multiple browsers (Edge and Chrome), and two mice.  The odd thing is I logged in with my account on someone else's machine and it worked so it doesn't seem to be related to my login.  The drag feature also works for my colleagues on a Mac and a Dell XPS. I'm on a Lenovo Yoga.