Hi:
I have the same problem as you. I have verified that if I put the component inside a v-for it does not work. With this check I assumed that ref must be an array not a single value. (https://stackoverflow.com/questions/52086128/vue-js-ref-inside-the-v-for-loop)
So my solution was:
  <template v-for = “(item, i) in items”>
…
   <q-popup-proxy ref = “MyReferences”>
          <q-date
             …
             @input = “() => $ refs.MyReferences [i] .hide ()”
          />
  </q-popup-proxy>
…
</template>
Where i = 0,1,2, …
I do not know if in your case this helps you, but to me your doubt helped me to solve mine, thanks