Unhandled exception after updating from 9.2.0 to 9.3.0; issues with adapting to App.razor #10527

We're currently updating our framework version from 8.2.2, following the migration guides step by step.

Upon updating from 9.2.0 to 9.3.0, the following Exception occurs:

System.ArgumentException: The path in 'value' must start with '/'. (Parameter 'value')
   at Microsoft.AspNetCore.Http.PathString..ctor(String value)
   at Microsoft.AspNetCore.Mvc.Routing.UrlHelperBase.Content(HttpContext httpContext, String contentPath)
   at Volo.Abp.AspNetCore.Mvc.UI.Bundling.TagHelpers.AbpTagHelperScriptService.AddHtmlTag(ViewContext viewContext, TagHelper tagHelper, TagHelperContext context, TagHelperOutput output, BundleFile file, IFileInfo fileInfo)
   at Volo.Abp.AspNetCore.Mvc.UI.Bundling.TagHelpers.AbpTagHelperResourceService.ProcessAsync(ViewContext viewContext, TagHelper tagHelper, TagHelperContext context, TagHelperOutput output, List`1 bundleItems, String bundleName)
   at Volo.Abp.AspNetCore.Mvc.UI.Bundling.TagHelpers.AbpBundleTagHelperService`2.ProcessAsync(TagHelperContext context, TagHelperOutput output)
   at Microsoft.AspNetCore.Razor.Runtime.TagHelpers.TagHelperRunner.<RunAsync>g__Awaited|0_0(Task task, TagHelperExecutionContext executionContext, Int32 i, Int32 count)
   at Ipoox.Omm.Blazor.Pages.Pages__Host.<>c__DisplayClass22_0.<<ExecuteAsync>b__1>d.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Razor.Runtime.TagHelpers.TagHelperExecutionContext.SetOutputContentAsync()
   at Ipoox.Omm.Blazor.Pages.Pages__Host.ExecuteAsync() in C:\Users\LBA\source\repos\omm\src\Ipoox.Omm.Blazor\Pages\_Host.cshtml:line 16
   at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderPageCoreAsync(IRazorPage page, ViewContext context)
   at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderPageAsync(IRazorPage page, ViewContext context, Boolean invokeViewStarts)
   at Microsoft.AspNetCore.Mvc.Razor.RazorView.RenderAsync(ViewContext context)
   at Microsoft.AspNetCore.Mvc.ViewFeatures.ViewExecutor.ExecuteAsync(ViewContext viewContext, String contentType, Nullable`1 statusCode)
   at Microsoft.AspNetCore.Mvc.ViewFeatures.ViewExecutor.ExecuteAsync(ViewContext viewContext, String contentType, Nullable`1 statusCode)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResultFilterAsync>g__Awaited|30_0[TFilter,TFilterAsync](ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResultExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.ResultNext[TFilter,TFilterAsync](State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeResultFilters>g__Awaited|28_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeNextResourceFilter>g__Awaited|25_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Rethrow(ResourceExecutedContextSealed context)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.Next(State& next, Scope& scope, Object& state, Boolean& isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeFilterPipelineAsync>g__Awaited|20_0(ResourceInvoker invoker, Task lastTask, State next, Scope scope, Object state, Boolean isCompleted)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Logged|17_1(ResourceInvoker invoker)
   at Microsoft.AspNetCore.Mvc.Infrastructure.ResourceInvoker.<InvokeAsync>g__Logged|17_1(ResourceInvoker invoker)
   at Microsoft.AspNetCore.Routing.EndpointMiddleware.<Invoke>g__AwaitRequestTask|7_0(Endpoint endpoint, Task requestTask, ILogger logger)
   at Volo.Abp.AspNetCore.Serilog.AbpSerilogMiddleware.InvokeAsync(HttpContext context, RequestDelegate next)
   at Microsoft.AspNetCore.Builder.UseMiddlewareExtensions.InterfaceMiddlewareBinder.<>c__DisplayClass2_0.<<CreateMiddleware>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Volo.Abp.AspNetCore.Auditing.AbpAuditingMiddleware.InvokeAsync(HttpContext context, RequestDelegate next)
   at Volo.Abp.AspNetCore.Auditing.AbpAuditingMiddleware.InvokeAsync(HttpContext context, RequestDelegate next)
   at Microsoft.AspNetCore.Builder.UseMiddlewareExtensions.InterfaceMiddlewareBinder.<>c__DisplayClass2_0.<<CreateMiddleware>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Swashbuckle.AspNetCore.SwaggerUI.SwaggerUIMiddleware.Invoke(HttpContext httpContext)
   at Swashbuckle.AspNetCore.Swagger.SwaggerMiddleware.Invoke(HttpContext httpContext, ISwaggerProvider swaggerProvider)
   at Microsoft.AspNetCore.Authorization.AuthorizationMiddleware.Invoke(HttpContext context)
   at Volo.Abp.AspNetCore.Uow.AbpUnitOfWorkMiddleware.InvokeAsync(HttpContext context, RequestDelegate next)
   at Microsoft.AspNetCore.Builder.UseMiddlewareExtensions.InterfaceMiddlewareBinder.<>c__DisplayClass2_0.<<CreateMiddleware>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Volo.Abp.AspNetCore.ExceptionHandling.AbpExceptionHandlingMiddleware.InvokeAsync(HttpContext context, RequestDelegate next)
   at Volo.Abp.AspNetCore.ExceptionHandling.AbpExceptionHandlingMiddleware.InvokeAsync(HttpContext context, RequestDelegate next)
   at Microsoft.AspNetCore.Builder.UseMiddlewareExtensions.InterfaceMiddlewareBinder.<>c__DisplayClass2_0.<<CreateMiddleware>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Volo.Abp.AspNetCore.MultiTenancy.MultiTenancyMiddleware.InvokeAsync(HttpContext context, RequestDelegate next)
   at Microsoft.AspNetCore.Builder.UseMiddlewareExtensions.InterfaceMiddlewareBinder.<>c__DisplayClass2_0.<<CreateMiddleware>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Builder.ApplicationBuilderAbpOpenIddictMiddlewareExtension.<>c__DisplayClass0_0.<<UseAbpOpenIddictValidation>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Authentication.AuthenticationMiddleware.Invoke(HttpContext context)
   at Volo.Abp.AspNetCore.Security.AbpSecurityHeadersMiddleware.InvokeAsync(HttpContext context, RequestDelegate next)
   at Microsoft.AspNetCore.Builder.UseMiddlewareExtensions.InterfaceMiddlewareBinder.<>c__DisplayClass2_0.<<CreateMiddleware>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Volo.Abp.AspNetCore.Tracing.AbpCorrelationIdMiddleware.InvokeAsync(HttpContext context, RequestDelegate next)
   at Microsoft.AspNetCore.Builder.UseMiddlewareExtensions.InterfaceMiddlewareBinder.<>c__DisplayClass2_0.<<CreateMiddleware>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Localization.RequestLocalizationMiddleware.Invoke(HttpContext context)
   at Microsoft.AspNetCore.RequestLocalization.AbpRequestLocalizationMiddleware.InvokeAsync(HttpContext context, RequestDelegate next)
   at Microsoft.AspNetCore.Builder.UseMiddlewareExtensions.InterfaceMiddlewareBinder.<>c__DisplayClass2_0.<<CreateMiddleware>b__0>d.MoveNext()
--- End of stack trace from previous location ---
   at Microsoft.AspNetCore.Diagnostics.DeveloperExceptionPageMiddlewareImpl.Invoke(HttpContext context)

What we did for this to occur:

• We ran abp update -v 9.3.0 on our 9.2.0 solution
• Additionally, updated Blazorise from 1.7.6 to 1.8.8
• We're using a customized old Lepton Theme, which we suspect to be an issue. Further information below.

What we've tried: Update our solution according to this thread, i.e. replace _Host.cshtml with App.razor according to 10.1.0 template. This partially resolved the issue - the above exception is no longer thrown.

Problems that remain:

• We cannot find a suitable value for AuthorizeRouteView.DefaultLayout in the new Routes.razor. The 10.1.0 template, using LeptonX theme, injects IOptions<LeptonXThemeBlazorOptions> and uses it's Layout property which the old Lepton theme does not seem to have an analogous way of doing
• The code in Index.razor generated by abp update has the error 'PageLayout' does not contain a definition for 'ShowToolbar'
• The navbar is missing in the application, although we assume this is due to one of the problems described above.

How can we resolve these problems? Is there something wrong with our approach of replacing _Host.cshtml with App.razor? Do we have to migrate from the old Lepton theme?