Hi,
I am afraid I am not sure of the point of this page.
This undefined behavior does not seem to related to the shared_lock, but rather related to any lock. This page just seems to be the redundant explanation of ordinary undefined behavior?
Course: Modern C++ Concurrency: Get the most out of any machine - Learn Interactively
Lesson: Types of Locks: std::shared_lock - Modern C++ Concurrency: Get the most out of any machine