After some more research I found a way to access the getter by importing the store and going that way. Maybe not the correct way but it will do until we move to Pinia.

import { store } from '../..'

[GET_MERGED_ISSUES]: (state) => (position) => {
    ...
    let positionIssue = store.getters[GET_POSITION_ISSUE](position)
    ...
  }