Hi Adam,
What is your Light map resolution set to for this object? If you didn’t adjust it, it will be 32 by default. Try setting this to something like 64 or 128 and see if we get the same results.
Also, Did this happen after you built lighting or was it this way initially? If it was this was initially this could be something with the mesh rather than lightmaps.
Let me know how that works out. If this doesn’t fix it I could take a look at the mesh for you if you want to attach a link for it here or if you don’t want to make it public you can send a link via the forums to me in a private message.
Thank you!
Tim