Example of a bug in Vuetify that causes the fill-height class to disappear.
I built a barebones application useing vue/cli@5.0.0-beta.2 with the following commands:
vue create vuetify-missing-fill-height
vue add vuetify
This created an app with vue@2.6.14 and vuetify@2.5.6.
Then I simply changed the content of App.vue so that <v-main> contained the grid example from the docs (also on GitHub). And then I removed everything from the v-app-bar except the logo.
Now, when you run the dev server, the <v-progress-circular> components are not vertically centered over the <v-img> components when loading. Instead, they are positioned at the top. This is because the fill-height class, which is set on the <v-row> component containing the <v-progress-circular>, does not exist. I have no idea why it is missing. But, if we place the <v-spacer> back in the <v-app-bar>, then fill-height returns and everything is positioned correctly.
To see the <v-progress-circular> components position correctly, uncomment line 20 of App.vue. With the inspector, you will see that the fill-height class has magically returned.
TL;DR: Removing <v-spacer> make the fill-height class disappear from the stylesheet.
npm install
npm run serve