Since the number of passengers decreased at stay home, the number of mails tended to overflow as a result of reducing convoys.
So I tried destroying the staging inn and making it a post office.
Then the flat slope underneath also destroyed just as I destroyed city building. (´・ω・｀)
The slope was created when I was still rich.
Ranran, who suffers from financial difficulties, cannot make a flat slope again... ::'(
Slopes on built up tiles don't seem to be stored.
If you remove any building, the "default" slope will be restored, i.e. the one you get when using the "restore natural slope" tool.
I do not think that this is a bug; this is the basic behaviour inherited from Standard.