I'm posting this here in hopes it might be helpful to someone at some point.
I noticed that when viewing my entire library in Lightroom, if I used the Metadata filter and had "Camera" as one of the fields, Lightroom would not load the camera information. It worked if I selected just a collection or folder. After some analysis, I found the problem to be related to a few photos that had corrupt or empty Camera information in the EXIF data. This was shown in Lightroom by having a null value for Camera (as compared to the normal "Unknown" or "Unknown Camera"). I had to manually go through each folder to find the problem images. I used a tool called Exif Pilot to edit the information for those files and put "Unknown Camera" in the camera field. That did the trick and now it works! When doing this make sure you have expanded all stacks to find the problem images.