这是由于地图实例是异步加载的当.vue文件开始加载地图的时候地图还没完成初始化而获取不到地图实例造成的。

错误代码
main.js（初始化地图）

import Vue from 'vue'
import VueAMap from 'vue-amap'
Vue.use(VueAMap);
VueAMap.initAMapApiLoader({
    key: '3b576d3486dc84adc303919ebc399dba',
    plugin: ['AMap.Autocomplete', 'AMap.PlaceSearch','AMap.Scale', 'AMap.OverView', 'AMap.ToolBar', 'AMap.MapType', 'AMap.Geolocation','AMap.Geocoder', 'AMap.AMapManager', 'AMap.Marker'],
    v: '1.4.4'
});

.vue组件中（直接使用）

<template>
  <div class="about">
      <div class="amap-page-container">
          <el-amap vid="amap" :zoom="zoom" :center="center" class="amap-demo">
            <!-- <el-amap-ground-image v-for="groundimage in groundimages" :url="groundimage.url" :bounds="groundimage.bounds" :events="groundimage.events"></el-amap-ground-image> -->
            <el-amap-marker 
              v-for="(marker, index) in markers"
              :position="marker.position" 
              :visible="marker.visible" 
              :draggable="marker.draggable" 
              :vid="index">
            </el-amap-marker>
          </el-amap>
      </div>
  </div>
</template>

<script>
  import n from '../assets/n'
  const exampleComponents = {
      props: ['text'],
      template: `<div>text from  parent: {{text}}</div>`
  }
  export default {
    data () {
        return{
            a: 5,
            ops: {
                bar: {
                    background: 'rgb(24, 144, 255)',
                    size: '0'
                },
                rail: {
                    border: '0',
                    size: '0'
                },
                scrollButton: {
                    enable: true,
                    background: '#cecece'
                }
            },
            zoom: 7,
            center: [121.5273285, 31.21515044],
            markers: [
              {
                position: [121.5273285, 31.21515044],
                visible: true,
                draggable: false,
                template: '<span>1</span>',
              },
              {
                position: [121.5273285, 35.21515044],
                visible: true,
                draggable: false,
                template: '<span>2</span>',
              },
              {
                position: [121.5273285, 39.21515044],
                visible: true,
                draggable: false,
                template: '<span>3</span>',
              }
            ],
        }
    },
  }
</script>

解决办法：不在main.js中初始化地图，而是在要使用地图的组件中初始化地图（并且是在vue实例之前初始化）

<script>
  import VueAMap from 'vue-amap'
  VueAMap.initAMapApiLoader({
    key: '3b576d3486dc84adc303919ebc399dba',
    plugin: ['AMap.Autocomplete', 'AMap.PlaceSearch','AMap.Scale', 'AMap.OverView', 'AMap.ToolBar', 'AMap.MapType', 'AMap.Geolocation','AMap.Geocoder', 'AMap.AMapManager', 'AMap.Marker'],
    v: '1.4.4'
  });
  import n from '../assets/n'
  const exampleComponents = {
      props: ['text'],
      template: `<div>text from  parent: {{text}}</div>`
  }
  export default {
    data () {
        return{
            zoom: 7,
            center: [121.5273285, 31.21515044],
            markers: [
              {
                position: [121.5273285, 31.21515044],
                visible: true,
                draggable: false,
                template: '<span>1</span>',
              },
              {
                position: [121.5273285, 35.21515044],
                visible: true,
                draggable: false,
                template: '<span>2</span>',
              },
              {
                position: [121.5273285, 39.21515044],
                visible: true,
                draggable: false,
                template: '<span>3</span>',
              }
            ],
        }
    }
  }
</script>

#2019.11.28 
以为网上的朋友咨询了我发现博客有的地方没有写清楚这里补充一下

无论在页面还是main.js都要引入
import Vue from 'vue'
import VueAMap from 'vue-amap'
Vue.use(VueAMap);