Flutter is not clearing rendered widgets, only re-painting - flutter

Question

I am having a Scaffold with a floatingActionButton. Inside I have an inappwebview which displays some webpage. The floatingActionButton is displayed in the front above the webview. Also I show some dialog for a second.
Everything worked fine until yesterday. I upgraded flutter and I suddenly experienced weird behaviour which is why i downgraded flutter again. But I still got the same problem. All the stuff that is rendered above is never cleared and just re-painted all the time, which leads to dark shadows and never disappearing dialog windows.
Here you can see the dark shadow around the floatingActionButton and the bottomBar. Also the "<3 + Karma" badge does not disappear anymore.
The weird thing is, that I did not change anything. On my other machine everything still builds fine. There I use the same code, same package versions in my pubspec.yaml and also the same flutter/dart version.
I am really puzzled here. I can't seem to build a new app version without this bug on my main desktop machine.
This is my currently used flutter version:
Flutter 2.10.2 • channel unknown • unknown source
Framework • revision 097d3313d8 (3 months ago) • 2022-02-18 19:33:08 -0600
Engine • revision a83ed0e5e3
Tools • Dart 2.16.1 • DevTools 2.9.2
flutter doctor tells me, No issues found!
This is my code for reference:
return WillPopScope(
onWillPop: ArticleHandler().backButtonPressed,
child: Scaffold(
floatingActionButton: Visibility(
visible: _fabIsVisible,
child: FloatingActionButton(
onPressed: () {
webView.scrollTo(x: 0, y: 0, animated: true);
},
child: Icon(
Icons.arrow_upward,
color: Colors.white,
),
backgroundColor: Theme.of(context).primaryColor,
)),
floatingActionButtonLocation: MarginEndFloatFABLocation(),
floatingActionButtonAnimator: NoFABAnimation(),
appBar: TopBar(widget.articlePreview.url),
body: Builder(builder: (BuildContext context) {
return Container(
child: Column(
children: <Widget>[
progress < 1.0
? Container(
height: 3,
child: LinearProgressIndicator(
value: progress,
backgroundColor: Colors.white,
valueColor: AlwaysStoppedAnimation<Color>(Theme.of(context).primaryColor),
))
: Container(height: 0),
Expanded(
child: InAppWebView(
initialOptions: InAppWebViewGroupOptions(
android: AndroidInAppWebViewOptions(useHybridComposition: true),
crossPlatform: InAppWebViewOptions(
//cacheEnabled: false, // uncomment this line to clean cache on open
)),
onWebViewCreated: (InAppWebViewController controller) {
webView = controller;
},
onProgressChanged: (InAppWebViewController controller, int progress) {
setState(() {
this.progress = progress / 100;
});
},
onOverScrolled: (InAppWebViewController controller, int x, int y, bool clampedX, bool clampedY) {
// maybe show karma badge
},
onScrollChanged: (InAppWebViewController controller, int x, int y) async {
if (y > 0) {
if (!_fabIsVisible) {
setState(() {
_fabIsVisible = true;
});
}
} else {
if (_fabIsVisible) {
setState(() {
_fabIsVisible = false;
});
}
}
})),
BottomTagBar(),
],
));
}),
));