I’m having problems with both right and left drags being dropped early. I am using a Logitech G400, which seems to be a popular brand in this thread.
I tried to reproduce this problem for about a half hour in explorer, and found that if I release some pressure when dragging, but not so much that the mouse audibly un-clicks, the OS will drop the input. What’s worse is that if I put full pressure back on, the right click will (sometimes?) not engage. I must fully release the right mouse button before it will work again. Obviously this is pretty terrible when you are in the middle of combat.
There could still be some problem with GW2, but I suggest if you have some minutes to try to test on the desktop with varying pressures to try to rule out a hardware related issue.