I’m using Admob sdk to access ads, and I use app open ads, but now there’s a problem where ads don’t appear properly, or are transparent.
I got the code steps exactly the same as the AD case, showing an AD and caching an AD. When I killed the app, the process did not change. When I opened the app again and needed to show the cache AD, I reported an error about webview, as follows:

Application attempted to call on a destroyed WebView
java.lang.Throwable
  at org.chromium.android_webview.AwContents.t(chromium-TrichromeWebViewGoogle6432.aab-stable-647813533:10)
  at com.android.webview.chromium.WebViewChromium.setBackgroundColor(chromium-TrichromeWebViewGoogle6432.aab-stable-647813533:46)
  at android.webkit.WebView.setBackgroundColor(WebView.java:3023)
  at com.google.android.gms.ads.internal.webview.ab.ae(:com.google.android.gms.policy_ads_fdr_dynamite@)
  at com.google.android.gms.ads.internal.overlay.l.x(:com.google.android.gms.policy_ads_fdr_dynamite@)
  at com.google.android.gms.ads.internal.overlay.l.d(:com.google.android.gms.policy_ads_fdr_dynamite)
  at com.google.android.gms.ads.internal.overlay.client.a.bV(:com.google.android.gms.policy_ads_fdr_dynamit5)
  at m.amo.onTransact(:com.google.android.gms.policy_ads_fdr_dynamite@)
  at android.os.Binder.transact(Binder.java:1169)
  at com.google.android.gms.internal.ads.zzazo.zzdc(SourceFile:8)
  at com.google.android.gms.internal.ads.zzbun.zzl(SourceFile:9)
  at com.google.android.gms.ads.AdActivity.onCreate(SourceFile:18)
  at android.app.Activity.performCreate(Activity.java:8538)
  at android.app.Activity.performCreate(Activity.java:8502)
  at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1437)
  at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:3878)
  at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:4043)
  at android.app.servertransaction.LaunchActivityItem.execute(LaunchActivityItem.java:101)
  at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:135)
  at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:95)
  at android.app.ActivityThread$H.handleMessage(ActivityThread.java:2437)
  at android.os.Handler.dispatchMessage(Handler.java:106)
  at android.os.Looper.loopOnce(Looper.java:211)
  at android.os.Looper.loop(Looper.java:300)
  at android.app.ActivityThread.main(ActivityThread.java:8294)
  at java.lang.reflect.Method.invoke(Native Method)
  at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:580)
  at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:1028)`

I m sure I got the code exactly like the example on the admob website