Here is the blog post from their blog:

"We are aware that some of you have been experiencing issues with streets that have offers attached to them. This is due to corrupt data which occurred when one of our databases went offline. We’ve tried fixing this without interrupting your game play, however to correct some inconsistencies we need to take the game offline for maintenance.

We expect the maintenance window to last between 4 – 8 hours from 8am, GMT Monday 26 October. During this maintenance window we will conduct a full review of the current data set to identify any inconsistencies.

There are 2 main inconsistencies we have identified with the current data set that we will resolve.

Firstly there are some streets that have been involved in the offer process that are currently in a state of 'limbo’. In this state you can see a street in your portfolio, you own it, but you cannot currently build on it. Once we have run our repairs you will be able to build again.

Secondly, some players own a street but it is not appearing in their property list, again due to lost data from database downtime.

Thank you for your patience and understanding as we work to improve the game."

So let's hope they'll fix the bugs.