Pixhawk 6c Lidar Lite v3 I2C issues

I recently built a new helicopter with a Holybro x500 v2 frame and a Pixhawk 6c FMU. I plan to add my Lidar Lite v3 to the frame. However, my first attempts were unsuccessful. I use an IC2 protocol with the same settings as my older drone with a Dropix-FMUv2. The lidar works great on the older frame, but the readings are erratic on the new frame with the Pixhawk 6c. Sometimes no readings are taken at all for seconds. The connections of the lidar are done according to Garmin’s manual (separate power supply). Both drones are flashed with the latest firmware 4.3.6. Can someone help me with this problem?