I believe this started when the new loading screens went live. So for the first few hours of the patch, everything could be pinged fine. But once the new loading screens went live, you are now no longer able to ping buffs/dragon/etc (but you can still ping items).
I asked in chat to make sure it wasn't just me. No one else was able to ping them.
EDIT: Reproduction rate is not 100%. If it happens in your game, it will be 100% for that game, for you. But it won't happen every game. I just played a game where all of us could ping objectives but our mid laner could not.