Failed to load Google Map properly on my app page

I have installed Ionic Native Google Maps plugin on my Ionic 4 app. Here is some information:

"@ionic-native/google-maps": "^5.5.0",
"cordova-plugin-googlemaps": "^2.6.2",
...
"cordova-plugin-googlemaps": {
        "API_KEY_FOR_ANDROID": (my api key),
        "API_KEY_FOR_IOS": (my api key),
        "PLAY_SERVICES_VERSION": "15.0.1",
        "ANDROID_SUPPORT_V4_VERSION": "27.+",
        "LOCATION_WHEN_IN_USE_DESCRIPTION": "This app wants to get your location while this app runs only.",
        "LOCATION_ALWAYS_USAGE_DESCRIPTION": "This app wants to get your location always, even this app runs in background."
}

and here is my implementation:
config.xml

<widget>
    <preference name="GOOGLE_MAPS_ANDROID_API_KEY" value='(my api key)' />
    <preference name="GOOGLE_MAPS_IOS_API_KEY" value='(my api key)' />
</widget>

page.ts

<ion-content color="background">
  <ion-grid>
    <ion-row>
      <ion-col size="12">
        <div id="map_canvas"></div>
      </ion-col>
    </ion-row>
 <ion-grid>
<ion-content>

page.scss

#map_canvas {
  min-height: 300px;
  height: 100%;
  padding-left: 15px;
  padding-right: 15px;
  border: 0.5px solid rgba(104, 112, 137, 0.5);
}

page.ts

import { GoogleMap, GoogleMaps, Environment } from '@ionic-native/google-maps/ngx';

export class Page implements OnInit {
   map: GoogleMap;
   constructor() { }
   ngOnInit() {
    this.platform.ready().then(() => this.loadMap());
   }
   loadMap() {
      Environment.setEnv({
        'API_KEY_FOR_BROWSER_RELEASE': (my api key),
        'API_KEY_FOR_BROWSER_DEBUG': (my api key),
      });
      this.map = GoogleMaps.create('map_canvas');
   }
}

But the map cannot be shown properly like:


It’s empty!

What can I do? My device is Android 10. Thank you.

ionic info

Ionic:

   Ionic CLI                     : 5.4.13
   Ionic Framework               : @ionic/angular 4.11.7
   @angular-devkit/build-angular : 0.803.21
   @angular-devkit/schematics    : 8.1.3
   @angular/cli                  : 8.1.3
   @ionic/angular-toolkit        : 2.0.0

Cordova:

   Cordova CLI       : 9.0.0 (cordova-lib@9.0.1)
   Cordova Platforms : android 8.1.0, browser 6.0.0, ios 5.1.1
   Cordova Plugins   : cordova-plugin-ionic-keyboard 2.2.0, cordova-plugin-ionic-webview 4.1.3, (and 10 other plugins)

Utility:

   cordova-res : 0.8.1
   native-run  : 0.3.0

System:

   Android SDK Tools : 26.1.1
   NodeJS            : v10.16.3
   npm               : 6.9.0
   OS                : Windows 10

I have solved my problem by placing map’s div outside any ion-element and it works!