I have Lightroom 2015 6.1 installed on a Mac running 10.11.6. I have a holiday folder with raw and same time jpeg files direct from the camera (August 2016) which all at the import resolution until recently. When viewing the thumbnails 2 nights ago I noticed that both raw and jpeg images went from a resolution of 4896-3264 pxs to 2495-1408 pxs. I was able to get the raw files back to the larger original size by doing a 'select all' reset all in the library mode. The same process did not work on the jpeg files. What is also strange is that when I view the images via finder in time machine mode, the jpegs are the smaller resolution ?? I normally shoot in raw and I could use the raw files and export them as jpegs. Downside is is that I loose the 'camera application' to each jpeg which gives it more zing that an unprocessed raw file. I know I can work on the raw files and achieve a better finish but thats not the point. There is a cause to this which I'd be grateful for any help please. PS adobe tech support via phone and chat (from India) has not resolved things. I think it was above their heads on this occasion and I could not go higher in the tech help unfortunately.