I’ve found the error!
The error was caused by npm +Windows 10, i think.
The rename of the temporary package.json didnot work and Files in Subfolder for ‘node_modules’ had become read-only.
Some Component (Quasar) were updated, others not (vue).
No Errors or Warnings.
After resetting attributes and updating npm + vue + quasar, its working
@benoitranque Thanks a lot, for your help.

The component code is that from the post at Nov 11. The whole project 37 Files (a little bit to much, i think).
I’ve tried out the same / above code in a complete new created (14.7) Project - the component itself works as expected
It seems that it has also nothing to do with sub-components (copied to the main component - failed).
Perhaps it’s a broken update problem. Update was made by ‘npm update quasar-framework’ and it shows 14.7.
What the appropriate way to update, i’ve read different answers in the forum, but nothing ‘qualified’ in the docu. The project origin was 14a.
Is there a way to check all (which) components are up to date?

Browser are chrome Version 62.0.3202.89 (64-Bit) and Firefox 56.0.2 (64-Bit)
theme: default mat
the q-input is between the q-field-tags as you can see

<q-field label="Some Label" helper="Some helper" error-label="Some error" labelWidth="3" :count="10" :error="error"> 
   <q-input v-model="text" color="primary"></q-input>
</q-field>

I think ‘helper’ and ‘count’ generates this line

CSS:  .q-field-no-input{  border-top: 1px solid rgba(0,0,0,0.12); }

The whole project ist very large, but the behavior is reproduceable also in a new project
It’s the example and only if ‘helper’ or ‘:count’ is used … (the dark theme hides it)

<template>
  <q-field label="Some Label" helper="Some helper" error-label="Some error" labelWidth=1 :count="10" :error="error"> 
    <q-input v-model="text" color="primary"/>
  </q-field>
</template>
<script>
  import 'quasar-extras/fontawesome'
  import {QField, QInput} from 'quasar'
  export default {
    components: {
      QField, QInput
    },
    data: function () {
      return {
      }
    }
  }
</script>
<style lang="stylus">
</style>

Using q-input in q-field like the example but without ‘dark’ generates double underlines. Its only when using ‘helper’ or ‘:count’. Is it a error in my environment, or wanted?
Is there a option that i can use only q-input like this?
Label: ______________
thanks a lot for help … and please understand, i am new to javascript , vue and quasar …