Since the update today I've got that bug, too. Never had anything like this. Guests are littering like being crazy in my zoo (without me having changed anything regarding to guestcount, walkingways, bins (there is one every 20 or so meters). I even gave each of my caretakers an upgrade and doubled their count - no change, guests are littering, caretakers are just walking by. Sometimes they pick up the litter, most times they don't.
Edit: Tried a few things:
1. It's affecting all my zoos (tried 3 differnt ones)
2. It seems to be the guests littering faster than before and/or the guests just ignoring the bins. Watched in the heatmap how fast little red circles are plopping up, as guests walk along.
3. Some guests get stuck when searching for a bin.
4. Some or all guests don't use the bins anymore.