Ok, that's a known issue with LND, but i thought it was patched. Thanks.
The encountered error is due to a protocol violation by the node your friend is running. At some point either the LND implemention was sending some gossip messages in the wrong order (a channel update before a channel announcement).
c-lightning v0.9.1-59-gd5cb0d8
If possible, please downgrade to the last release (git checkout v0.9.1). You are currently running master.
Hope LND and c-lightning implementations can coexist and communicate between each other
They are! That's why there is
a protocol 
I know @darosior is already taking care of opening an issue about this problem in Github. Many thanks @darosior!