Thank you for answering my question. I was just asking so I have more information to pass on
Please keep in mind that it's not a simple matter of flipping a switch or pushing a button and then the issue is fixed. We haven't been able to recreate the issue yet, but the information you've provided should help. If we find other players with this issue who can send us their save files then of course we will ask them to do so. I understand that it's frustrating and I sympathise with you, but please be patient.
Since you're playing in Sandbox Mode, maybe you can turn off animal sickness for now, so the Quarantine Centers won't be needed? You can then continue playing the game and building your zoos without this roadblock.