[Vuejs]-Unreliable data Vuex

From where are you trying to access this.getters.reservationsCurrentWeek ? If you are accessing getters from mutation and getters and mutations placed in one file you can use

mutations: {
  YOUR_MUTATION(state, {data, getters}) {
    console.log(getters);
  }
}

and then access getters. Or import getters from another file if it placed in separate file.