As Cletus has put, what you are seeing is normal and 100% deliberate, it is not a bug. LR has switched from displaying the embedded jpeg to applying its own version. After all, that is what LR is for.
BUT. Three stops? Really? What is the histogram (on the back of the camera)? Looking at the rear view monitor is only so good. The histogram is of the embedded jpeg (not the RAW), so presumably is fine (you are exposing to the right?). If the correction is always three stops, you can add that back on in a single command in LR (to all 2,000 images) in about two steps (select all, apply correction). You also have synchronise options, or you apply a chosen set of corrections to a whole bunch of images. That three stops suggests to me that you have some preset or something set up in LR which is applying a correction before you get started, eg on import.
All I can say is that from my experience w LR, it doesn't cause the image to be three stops under-exposed compared to the embedded jpeg for what I would call 'conventional' pictures. I'm assuming your wedding pictures are conventional, in the sense of how they are exposed. I would look for a cause in the way that you are using LR. Maybe others have different experiences.
Could somebody who knows more about this: does LR have its own version of D-Lighting? Some Adobe preset?
If you are deliberately under-exposing three stops (and some wedding photographers do, to hold blowing out the highlights of say a white dress), you might want to explore how to use an incident light meter. Incident light meters exist to get you out of that sort of problem. LR is still your friend by the way (if you are under-exposing by three stops), you will just have to get used to how it is helping you.
HTHs