HELP pictures are very pixelated in Lightroom but not on camera

I have never had this issue until this year, but I downloaded the photos off of my SD card (no problems with card, not pixelated), downloaded them to the photos app on my Mac, went through the photos, then tried to download them to lightroom. They look fine until you zoom in and they are super pixelated and there is no way around it. I have an external hard drive that I originally copied them to, but even then they are not downloading correctly. My lightroom is up-to-date and the pictures are all shot in RAW, even the photos say that. HELP ME PLEASE. I have a strict deadline to get these photos back to the client and I need them to not be messed up.