Version

5.3.4
not sure about the version_

Reproduction link

codesandbox.io

Steps to reproduce

1. Create basic app
2. Create basic store
3. Add store thorught new Vue({store: new Vuex.Store(storeObj)})
4. Add ANOTHER instance of vuex store

new Vue({
    anotherStore: new Vuex.Store(anotherStoreObj),
    store: new Vuex.Store(storeObj)
})

What is expected?

To show every store object or at least one that is defined under $store variable.

What is actually happening?

Now, in devtools you will only see state from vuex store that was init first.