Same thing happened to me last night. I had Cassandra Goth purchase Just Flowers and More in Bluewater Village. She had it up to Level 7. She went home to rest and tried to go back the next day but it wasn't in the list to visit. So I exited her house and went straight to Bluewater to see if the lot was still there. It was as if the lot never existed. I went back to the Goth house and Cassandra still had the deed in her inventory. Here is my theory on what probably happened.
When I tried to set the uniform for Cassandra, it wouldn't let me. That was when I noticed that all of my previously saved uniforms were gone from the list. That was the first problem I noticed that something was going wrong. This happened right after I used Merola's Mind Control Mirror to make my employees selectable. It went all downhill from there.
I heard after the fact that making employees selectable can corrupt your lot. I just reinstalled and I won't be doing that again...