I can't replicate it on the before save but since it's not happening to you as well, it might be just the same issue as this: https://answers.ea.com/t5/Bug-Reports/OPEN-Houses-Lots-disappear/td-p/4620279/jump-to/first-unread-message or this: https://answers.ea.com/t5/Bug-Reports/NEEDS-SAVES-Orange-Exclamation-signs-over-lots-Houses-disappear/m-p/10533991#M197875 and it's random.
It's fascinating that the buildings are gone but I was able to recover them so can you try if these steps work for you.
1. Enter the lot in build mode from the map
2. Back to map and travel there with a Sim.
3. See if the buildings are back.
The arms building is still gone but I can guess you can just replace that form the gallery.
Did you get any exceptions when it first disappeared ?
I didn't get any Last Exception Errors. The stalls did reappear after I followed the steps and the pub still missing. Thank you very much for taking the time to look into it.
