Please upload one of the files you are working with to Drop box and share the link to it in this thread.
What you are seeing usually means you are working with JPG files and not RAW files or if you opened that file in the Canon software first it has corrupted it in some way.
Take some shots using only RAW and then import them into a Newly created catalog and test.
If they work OK in a new catalog then re-open your original catalog and import those same shots into your original catalog and test. If you see the same behavior then Reset the LR Preferences and test.
Sounds like you switched your camera to shoot JPG.
Thanks! This is the answer! The RAW files were being ignored.
Read this and got up (midnight) and looked.
Sermed odd it was suddenly happening to both cameras.
You might of had the Filter bar open and selected to only show JPG images.