The probe had landed on Sunday morning in Korntal. At first undecided whether I should look for it, I finally got into the car and drove to the landing zone. When I arrived at 11:00 AM, the probe had already ceased transmitting. radiosondy.info recorded the last position of the probe at 48.8221N 9.13017E about 60m above the ground. The parachute was not completely open as the probe went down with 6.1 m/s.  The horizontal speed was around 2km/h which meant that the probe almost went vertically down. Arriving at the gps fix, I almost immediately found the parachute. I tried to follow the thread from the parachute to the probe using the binoculars to no avail. Maybe to probe had already been taken by somebody else. As I learned later, Florian had visited the landing site at 9:00. At that time, the probe was still transmitting.

Update on 2019-09-22

As I happened to be around, I checked the landing zone once more — this time I found the probe in about 8m height on a tree next to the tree in that the parachute had landed.

Update on 2019-09-29

I came back with a telescope rod and a hook. After extending the rod with a thick branch that I found lying around,  I first knocked down the probe from the tree branch. Now it was hanging freely and  I was able to attach a hook to it. Then I tried to pull the probe down. It moved about a meter down before hook slipped off the probe. A second attempt was successful. 

The thread had ripped apart in the process of the probe recovery. The  parachute was too high up and it seems to be firmly entangled with the tree. When  pulling down the probe, it  did not move at all.