Cannot handle deformable objects

Great Work! However, I tried with example [bunny](https://github.com/google-deepmind/mujoco/blob/main/model/flex/bunny.xml) with [shadow hand](https://github.com/google-deepmind/mujoco_mpc/tree/main/mjpc/tasks/shadow_reorient)
```

```
It gives me the following issue
```
grpc._channel._InactiveRpcError: <_InactiveRpcError of RPC that terminated with:
status = StatusCode.UNKNOWN
details = "Unexpected error in RPC handling"
debug_error_string = "UNKNOWN:Error received from peer ipv4:127.0.0.1:45789 {grpc_message:"Unexpected error in RPC handling", grpc_status:2}"
```
Do you have any idea about a quick fix?