When saving my map, the "saving" UI element stays up forever. If I exit to main menu then and reload the save, all items and animals on it will be gone.
It's pretty much the same saving issue that used to plague the game earlier in EA. I thought it was gone, but lo.
Interestingly, and it might just be superstition, but the issue seems to happen because I place a bunch of "substrate square 4m"s on a flat roof. Since discovering the bug, I've been able to do whatever else, but that specific action causes the map to become unsaveable. If any dev is interested in trying that out for themselves, they can ask me for a WeTransfer link.