This happens to me as well. Not often, but common enough to be noticeable. It’s not that guests leave; they disappear. I went from 6,0000 to 2,000 yesterday within 3 minutes. Not long after a horde of 4,000 started to attempt re-entry and it took 4 in game years for the guest satisfaction to climb back up to 80%+ because they were all in lines at the entrance. It’s not game breaking, but if it happens as much as you say, it would be. It gave my zoo the first negative months in over 100 years as refunds skyrocketed to 50 or 60k each year and average guest visit shrunk to 8 minutes. Many would turn around and create a logjam. I watched one time and my guests were stuck in the single entrance for 5 days leaving and entering. I believe something glitches in the game and it clears out guests to avoid a more serious problem, but I’m not sure.