SITL and gazebo crash on RTL

Hello,

I am using SITL + gazebo wtih the plugin https://github.com/khancyr/ardupilot_gazebo.

I want the drone to take off, fly trough some waypoints, land, and then do the same process again. When I set the mode to RTL the drone lands but when I set the mode again to guided, arm the motors and try to take off nothing happens. After a while I get the following message:

APM: Crash: Disarming
APM: Disarming motors
DISARMED

Everything works fine if I use only SITL without gazebo. So I am wondering if the UAV is crashing into the ground in gazebo or something. I am using the iris_ardupilot_runway.world. is there any detail that I do not know about?