Mission won't continue - Sensei Ishikawa stops suddenly

[Grumpy Gaijin]

In the mission where you need to find Sensei Ishikawa (the archer sensei) after being accused that you and him are attacking people, I have the problem that once I find him in near the watchtower (after defeating enemy archers), we ride together towards the place where there was an ambush.
After investigating, he continues the route and I follow him towards the training camp but right before turning to the right towards the camp... The music stops, Sensei stops and he just continues horseback riding gently towards the edge of the cliff. So I can't finish the mission...

Any solutions?