After updating to the latest Redux Dev Tools extension I am getting: "Symbol.observable as defined by Redux and Redux DevTools do not match."
This is a brand-new check and warning that was just added to the Redux DevTools code in the last few days:
https://github.com/reduxjs/redux-devtools/issues/1002#issuecomment-1011097465
If you're still using Redux 4.0.5 or earlier, it's possible that upgrading to Redux 4.1.x would fix this warning (because 4.1.0 removed the use of the symbol-observable polyfill).
That said, you should really be using our official Redux Toolkit package to set up the Redux store and write your Redux logic, rather than using the original core createStore method directly.