Hands-on Rust: not all monsters destroyed on collision (page 140)

After finishing the code at the end of Chapter 7 and running it, monsters sometimes don’t get destroyed on collision. Instead, the player disappears and only the monster displays until the two are at different locations again.

If I revert the code at the end of the “Moving Entities in a Turn-Based Game” section, I don’t see this behaviour.

I ran the downloaded sample code for that chapter and found the same thing.