Being disoriented due to his sembalance could easily be one of the reasons that he was in the way as Sapphire was attempting to escape from the collapsing tunnel. I was unaware that this was a fight that had happened in the previous RP but since this is a reboot with different characters we don't have to do it the same way. If no one has any problems I'm going to go ahead and post based on the stuff I said above.

We could also say that the tunnel was weakened severely by Gren and Kuhaku's attacks and Sapphire saw a chance to deal with the mech once and for all but the tunnel was so damaged that rather than just collapsing a ton of rock on the mech she destabilized the entire tunnel and Shiro screwed up her escape leading to both of them being caught by debris.