Several things about droning that you need to know before flying:

1. What and how RTH is triggered - This happens when the connection between Remote and drone is too weak. This is mainly when you fly out of line of sight, or have bad RF interference. In urban "condo" environment this is a bad combination as buildings will block line of sight, dense condo's will emit all sort of Wifi.
2. How RTH happens - When this happens what did you set your drone to do? Return to home point, stay at the same point until battery deplete ? First options requires a height to be set, and due your drone having front sensors if the height is not high enough in condo environment, it will try to fly around (usually unsuccessfully) or it will hover and land when battery reach 10%.

2. if you don't read the manual and understand everything before you fly, your next RM3-4k is going to encounter similar fate...

3. It is a case of theft if your drone was taken, you can report to police if you want.

4. Again, RTH conditions is the most important aspect of flying you must know in all circumstance.

5. Others - Know the wind conditions. Know that 10km is only achievable if you are flying in a straight visible line of sight, with NO interference. It is also illegal.

6. Know how much your battery can last and how it also affects RTH.