Jetbot RL example warnings and errors (Isaac Sim)

I am trying to run the Jetbot Reinforcement Learning example via: ./python.sh python_samples/jetbot/jetbot_train.py. After executing this Isaac Sim opens and for a while the training USUSALLY works. Meanwhile i contiuously get this warning:

2021-11-23 12:21:23 [392,989ms] [Warning] [omni.client.plugin] Main: usd_plugin: Could not open asset @omniverse://localhost/Library/Props/Road_Tiles/Parts/p4342p01.usd@ for reference on prim @anon:0x7f6a880021b0:World0.usd@,@anon:0x7f6a88002ff0:World0-session.usda@</World/Env/Tiles/Tile_07>. (recomposing stage on stage @anon:0x7f6a880021b0:World0.usd@ <0x7f6a88008210>)
2021-11-23 12:21:23 [392,989ms] [Warning] [omni.usd] Warning: in _ReportErrors at line 2830 of /buildAgent/work/ca6c508eae419cf8/USD/pxr/usd/usd/stage.cpp – Could not open asset @omniverse://localhost/Library/Props/Road_Tiles/Parts/p4342p01.usd@ for reference on prim @anon:0x7f6a880021b0:World0.usd@,@anon:0x7f6a88002ff0:World0-session.usda@</World/Env/Tiles/Tile_07>. (recomposing stage on stage @anon:0x7f6a880021b0:World0.usd@ <0x7f6a88008210>)

But after a while everything crashes, sometimes with error saying that the program was Killed, and sometimes saying that there was a Segmentation fault (core dumped).

Can you please help me solve this problem?

i also get this warning…