It was a nice stay.
However, the check in process is troubling.
We were trying to open the key as instructed, but to no success.
However to our surprise, the door was suddenly opened, and there were two guests who somehow can get in to our unit, ahead of us, with their own lock code.
They mistakenly assume our unit 11 C as their unit 15 C.
The other guests moved out, then after I called, the host management responded quickly and reset key lock.
But no answer to how the other guests can get in.