In the latest update to LRc, my photos in the lowest line of photos come up with an down arrow on them after I do any eidt to them. Then if I click on it it asks me to 'Save'. What is it saving? Is it actually modifying my original photo if I do select 'Save'? I do not understand since all edits are in the History panel, so why do I need to save them again? And, I certainly do not want to permanently change the original!
Did you have 'Automatically write changes to XMP' checked in the catalog settings before, and did it get unchecked? This sounds like the warning that the metadata on disk are different from the metadata in the catalog. You can safely ignore it, or turn on that setting again.
The update Metadata icon shows up when you make an edit/metadata change even if you never had "Automatically write changes to XMP" checked and there is no associated XMP file on disk. I just turn the icon OFF in Grid settings.