@Jeff and Rob. I would just like to make some further comments here. My experiences with faulty/flacky ram was some time ago and as far as I can recall, I experienced issues with corrupted raw files after import into Lightroom. The files would appear to import fine and then there would be a few files at random show corruption while attempting to do processing in the develop module. Sometimes I was able to delete the problem files and then re-import without problem and work with the reimported files without corruption issue. This would happen with a few files out of several hundred imported. A very random experience.
Even checking the ram with software designed to detect problems with the ram did not identify problems and it is only with a tecnican's assistance we were able to isolate the problem. The ram modules on my system were in pairs. We removed one of the pairs and ran the computer and eventually inditified that the problems only occured when one of the ram modules was present.
Installing new ram (both modules) rectified the problem. I had to go through this same process on two occasions.
Just a note. I do not write to .xmp and I do not use dng, just work with raw files direct from my Olympus and Panasonic cameras.
One other note, while I had problems related to Lightroom I also experienced some other problems with my system, shutting down unexpectedly. These problems also vanished when the ram was changed.