If a prompt such as "Do not store valuables in the locker" appears, the customer will still store valuables in the locker. Once lost, it is difficult to prove that the gym is at fault. If there is no such prompt, it means that the gym has made a mistake.
However, the Law on the Protection of Consumers' Rights and Interests stipulates that "consumers have the right to require the goods and services provided by business operators to meet the requirements of protecting personal and property safety."
I think I should file a claim. I read the news before that someone lost something in a bathing and fitness place, and finally the claim was successful. Of course, what they lost is more expensive, and the most troublesome process in the middle is how to prove that what they lost is what they said.
The gym should be compensated more or less.