If vacancy is at 0%, you increase supply and vacancy is still at 0% you should absolutely not expect prices to fall. In fact, you should expect exactly what is happening, the market will reevaluate it's prices upwards until vacancy reaches some positive value. It's economics 101. This software just makes the process hyper efficient, where as normally it'd be far slower as landlords would not have perfect information.

The only way to fix this is to drastically incentivize building to the point that supply is higher than demand.