It is not just in time keeping that mutable shared state is an issue, I have seen problems arising from it elsewhere as well in Python especially, but also in C and C++. Probably because Python is pass by reference implicitly, while C and C++ makes pointers/references more explicit, thus reducing the risk of such errors in the code.

There a few schools of thought about what should be done about it. One is to make (almost) everything immutable and hope it gets optimised away/is fast enough anyway. This is the approach taken by functional languages (and functional style programming in general).

Another approach is what Rust does: make state mutable xor shared. So you can either have mutable state that you own exclusively, or you can have read only state that is shared.

Both approaches are valid and helpful in my experience. As someone working with low level performance critical code, I personally prefer the Rust approach here.