I wouldn't say it's a lack of practice. Look and listen to your left hand... there's obviously tension there. You started practicing this a few days ago? I think you may be trying so hard to get it back to where it was when you originally learned it that you're pushing the limits of what you can do. Give it some more time, and I'm sure it will get to where you want it.
Don't do 5 performance takes back-to-back of this. Play it slow at least as much as you play it fast. Don't force it. Let the LH breathe a bit -- sometimes you start rushing.
Imagine if you will that the RH represents you going up into the sky and down to earth again many times in a row -- as if you are on a trampoline. In this scenario, the LH is the mode of takeoff from earth and back into the sky. It would be quite an abrupt flight from the earth if you were shot from a cannon. A trampoline, however, has some breathing room, and it is smooth.
Don't mess the rhythms up, but let the LH breath. It doesn't have to be loud all the time, either -- you're asking for your wrist to be busted if you do that.
Josh