Inside the mutation function, you are adding random values to the genes. This can cause the gene values to drift over time and in one of my examples, it is causing the value to go beyond the initial range of [-4, 4].

Maybe some checks need to be added for the range of acceptable values for example, instead of adding a random value between -1 and 1, maybe you can just pick a random value from the original range and use that as the mutated value.