Check the height, it seems a bit low and the Zebra might be able to jump over it.
Giraffes, zebras and elephants were all just walking through that patch of barrier. It was the same height as the rest of the barrier and above the minimum height for all three species. I did raise it a bit, and that seemed to fix the issue, so it's a head scratcher. For some reason the game saw the barrier as lower there from the animal side than my numbers said.
What I don't know is why it was fine the day before, with no escapes, but when I logged on to play the next evening I got multiple escapes within the first minute of play. This seems to happen to me sometimes with escapes, though. The game will be fine for hours, but I'll suddenly get a bunch happening one after the other when nothing appears to have changed in game.
Come to think of it, it's not unlike what happens with work zones where everything is balanced and all my animals are getting fed and cleaned out, so I can focus on something else in the game. Until suddenly all my keepers apparently go on strike or something
