CircularProgressIndicator breaks widget test

Question

I implemented a few snack bars, one of which contains a CircularProgressIndicator, for displaying loading messages.

The issue is that in emulator/device, the loading snack bar displays correctly, but in widget testing the snack bar doesn't display at all and is not found by the matcher.

More so, I built a test with golden_toolkit and added each type of snack bar as scenario, but if I include the loading snack bar no other snack bar is displayed anymore.

Here you can see the method which builds the snack bar:

void showLoadingSnackBar({
    Key? key,

    /// The message displayed to the user.
    required String message,

    /// The value of [SnackBar.behavior].
    SnackBarBehavior? behavior,

    /// The value of [SnackBar.width].
    double? width,
  }) {
    final colorScheme = Theme.of(this).colorScheme;
    final foregroundColor = colorScheme.onInverseSurface;
    FoSnackBar.message(
      key: key ?? const ValueKey("FoLoadingSnackBar"),
      behavior: behavior ?? (isIOS ? SnackBarBehavior.floating : null),
      width: width ?? (isIOS ? 250 : null),
      message: message,
      duration: 60,
      icon: SizedBox(
        height: 24,
        width: 24,
        child: Center(
          child: CircularProgressIndicator.adaptive(
            strokeWidth: 2,
            valueColor: AlwaysStoppedAnimation<Color>(foregroundColor),
          ),
        ),
      ),
    ).show(this);
  }

The FoSnackBar.message constructor:

factory FoSnackBar.message({
    Key? key,

    /// The message displayed to the user.
    required String message,

    /// Icon showed at the end of the snackbar.
    Widget? icon,

    /// The value of [SnackBar.behavior].
    SnackBarBehavior? behavior,

    /// The value of [SnackBar.backgroundColor].
    Color? backgroundColor,

    /// The text style of the [message].
    TextStyle? messageStyle,

    /// How many seconds is the message displayed.
    int? duration,

    /// The value [SnackBar.width].
    double? width,
  }) =>
      FoSnackBar(
        key: key,
        behavior: behavior,
        width: width,
        backgroundColor: backgroundColor,
        duration: Duration(seconds: duration ?? 4),
        content: Row(
          mainAxisAlignment: MainAxisAlignment.spaceBetween,
          children: [
            Flexible(
              child: Text(message, style: messageStyle),
            ),
            if (icon != null) icon,
          ],
        ),
      );

showLoadingSnackBar is a method in an extension on BuildContext, for easy access.

You can see the atached images which are without/with "Loading" snack bar.

System specifications:

Flutter (Channel stable, 3.7.12, on KDE neon 5.27 5.19.0-40-generic, locale ro_RO.UTF-8)
• Flutter version 3.7.12 on channel stable at /path/to/flutter
• Upstream repository https://github.com/flutter/flutter.git
• Framework revision 4d9e56e694 (3 days ago), 2023-04-17 21:47:46 -0400
• Engine revision 1a65d409c7
• Dart version 2.19.6
• DevTools version 2.20.1

Already did flutter clean and pub get. Anyone has any ideeas why is this happening?