Added a unit test to repro the issue

src/Microsoft.AspNetCore.Razor.Language/Legacy/TagHelperParseTreeRewriter.cs

@@ -488,7 +488,7 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
 
         private void ValidateParentAllowsContent(Span child, ErrorSink errorSink)
         {
-            if (HasAllowedChildren())
+            if (child.Kind == SpanKindInternal.Comment || HasAllowedChildren())
             {
                 var content = child.Content;
                 if (!string.IsNullOrWhiteSpace(content))

test/Microsoft.AspNetCore.Razor.Language.Test/Legacy/TagHelperParseTreeRewriterTest.cs

@@ -1108,6 +1108,43 @@ namespace Microsoft.AspNetCore.Razor.Language.Legacy
             EvaluateData(descriptors, documentContent, (MarkupBlock)expectedOutput, (RazorDiagnostic[])expectedErrors);
         }
 
+        [Fact]
+        public void Rewrite_AllowsCommentsAsChildren()
+        {
+            // Arrangestring documentContent,
+            IEnumerable<string> allowedChildren = new List<string> { "b" };
+            string literalPrefix = "";
+            string commentOutput = $"<!--Hello World-->";
+            string expectedOutput = $"<p>{literalPrefix}{commentOutput}<b>asdf</b></p>";
+
+            var pTagHelperBuilder = TagHelperDescriptorBuilder
+                .Create("PTagHelper", "SomeAssembly")
+                .TagMatchingRuleDescriptor(rule => rule.RequireTagName("p"));
+            foreach (var childTag in allowedChildren)
+            {
+                pTagHelperBuilder.AllowChildTag(childTag);
+            }
+
+            var descriptors = new TagHelperDescriptor[]
+            {
+                    pTagHelperBuilder.Build()
+            };
+
+            var factory = new SpanFactory();
+            var blockFactory = new BlockFactory(factory);
+
+            var expectedMarkup = new MarkupBlock(
+                new MarkupTagHelperBlock("p",
+                    factory.Markup($"{literalPrefix}{commentOutput}")));
+
+            // Act & Assert
+            EvaluateData(
+                descriptors,
+                expectedOutput,
+                expectedMarkup,
+                Array.Empty<RazorDiagnostic>());
+        }
+
         [Fact]
         public void Rewrite_UnderstandsNullTagNameWithAllowedChildrenForCatchAll()
         {