Fixed the issue dotnet#22042 & added a UITest

src/Controls/samples/Controls.Sample.UITests/Issues/Issue22042.xaml

@@ -0,0 +1,26 @@
+<?xml version="1.0" encoding="utf-8" ?>
+<ContentPage xmlns="http://schemas.microsoft.com/dotnet/2021/maui"
+             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
+             x:Class="Maui.Controls.Sample.Issues.Issue22042"
+             Title="Issue22042">
+
+    <ContentPage.Resources>
+        <RadialGradientBrush x:Key="PurpleGradiant"
+                         Center="0.8,0.5">
+            <GradientStop Color="#AD27FF"
+                          Offset="0.25" />
+            <GradientStop Color="#4447FE"
+                          Offset="0.75" />
+        </RadialGradientBrush>
+    </ContentPage.Resources>
+
+    <Border x:Name="border"
+            VerticalOptions="Center"
+            AutomationId="border"
+            StrokeThickness="2">
+        <Label Text="Hello, World!" />
+        <Border.GestureRecognizers>
+            <TapGestureRecognizer Tapped="TapGestureRecognizer_Tapped"/>
+        </Border.GestureRecognizers>
+    </Border>
+</ContentPage>

src/Controls/samples/Controls.Sample.UITests/Issues/Issue22042.xaml.cs

@@ -0,0 +1,26 @@
+using Microsoft.Maui.Controls;
+using Microsoft.Maui.Controls.Xaml;
+using Microsoft.Maui.Graphics;
+
+namespace Maui.Controls.Sample.Issues;
+
+[XamlCompilation(XamlCompilationOptions.Compile)]
+[Issue(IssueTracker.Github, 22042, "[Android] Border Stroke GradiantBrush can only switch to another gradiantbrush", PlatformAffected.Android)]
+
+public partial class Issue22042 : ContentPage
+{
+	private Brush _gradiantPurpleBrush => Resources.TryGetValue("PurpleGradiant", out object laColor) ? (Brush)laColor : null;
+
+	public Issue22042()
+	{
+		InitializeComponent();
+	}
+
+	private void TapGestureRecognizer_Tapped(object sender, TappedEventArgs e)
+	{
+		if (border.Stroke == _gradiantPurpleBrush)
+			border.Stroke = Colors.Red;
+		else
+			border.Stroke = _gradiantPurpleBrush;
+	}
+}

src/Controls/tests/UITests/Tests/Issues/Issue22042.cs

@@ -0,0 +1,31 @@
+using NUnit.Framework;
+using UITest.Appium;
+using UITest.Core;
+
+namespace Microsoft.Maui.AppiumTests.Issues
+{
+	public class Issue22042 : _IssuesUITest
+	{
+		public Issue22042(TestDevice device) : base(device)
+		{
+		}
+
+		public override string Issue => "[Android] Border Stroke GradiantBrush can only switch to another gradiantbrush";
+
+		[Test]
+		public void BorderCollorShouldChange()
+		{
+			this.IgnoreIfPlatforms(new TestDevice[] { TestDevice.iOS, TestDevice.Mac, TestDevice.Windows });
+
+			App.WaitForElement("border");
+
+			//Applies a gradient
+			App.Click("border");
+
+			//Applies a solid color
+			App.Click("border");
+
+			VerifyScreenshot();
+		}
+	}
+}

src/Core/src/Graphics/MauiDrawable.Android.cs

@@ -155,6 +155,7 @@ public void SetBorderColor(AColor? borderColor)
 
 			_borderColor = borderColor;
 
+			InitializeBorderIfNeeded();
 			InvalidateSelf();
 		}
 
@@ -183,6 +184,7 @@ public void SetBorderBrush(SolidPaint solidPaint)
 		{
 			_invalidatePath = true;
 			_borderColor = null;
+			_borderPaint = null;
 
 			var borderColor = solidPaint.Color == null
 				? (AColor?)null