On LR 6.14
I finally decided to get down to some keyword tidying up, only to discover that "Keywording" in LR 6.14 standalone seems to be completely broken (at least. on my machine).
Even with only one image selected, if I apply a keyword to that image the keyword is applied to "All Photographs". If I close/reopen LR then keywords show correctly, until I add a keyword to another image.
Obviously, to close/reopen LR every time I keyword an image is unworkable.
I've been a LR user since day one and have never encountered this problem.
Triple-check that you only have one photo selected. Assuming so, try resetting LR's preferences: https://www.lightroomqueen.com/articles-page/how-do-i-reset-lightrooms-preferences/ . That often fixes things when LR's user interface goes wonky.