This is usually a result of a minuscule typo.
For instance, if you are importing your modules like import Vue from 'vue', import Vuex from 'vuex'.
Go through your files and check where you used from 'Vue' or from 'Vuex' – make sure to use the exact same capitals (uppercase letters) as in your import statements.
The error descriptions should have been written more clearly, but what I explained has been the cause of my problem each time for this error on webpack commands.