Well, your refrigerator should easily last 24 hours if it's running on propane. Possible reasons why it didn't:
1) Your batteries were already run down. Even when running on propane some
12V power is required.
2) You're out of propane or the valve which should automatically switch between tanks when one is empty is faulty. Also, it's possible that the transfer valve tried to switch to the second tank and the supply valve on that tank was turned off.
3)You've selected the wrong operating mode for your fridge. I'm not sure if the 2019 FC has a 2-way or 3-way fridge. If it's a 3 way and you have
12V operation selected it will run down the battery in a hurry.
4) The fridge is broken or not operating properly.
Do you have the standard batteries that come stock from Airstream? Also, you say you don't think you have solar. If you're not sure, find a place where you can look down on the roof of your trailer. You'll either see solar panels or not.