Reset Vuetify form validation

resetValidation() will clear validation errors only, reset() will also clear input fields.

Example from docs uses:

this.$refs.form.reset()

Note that while reset() clears validation, it clears input as well.
You can follow this issue to see further updates on this.

So you can perhaps watch dialog value and reset the form:

watch: {
    dialog() {
        this.$refs.form.reset()
    }
}