Hiya,
So it seems like for most of the save files we were sent, there are overlapping educational speakers; this means that guests who walk into this overlapped area have a rapid drop in happiness - causing them to leave and want their money back.
Please check the Education heatmap, and if there's anything red in there: fix it!
Also, if you're running a bad zoo in general, that could cause a lot of unhappy guests too: not enough shops, too much litter, and expensive tickets; also, not having enough shops or having them all in one area only, and staff facilities being far away. Be sure to optimise your zoos in terms of placement: it's important!
We'll continue to look into other possibilities in the meantime

Cheers!
Hopefully that helps!!