Issue with Azure Functions Flex deployment: Function triggers synchronization fails

Question

Having issues when deploying .NET 9 Isolated Function App to Flex Consumption. The app gets packaged and deployed to blob storage, I can see it there. But looking at the portal->my-function-app->Functions overview (where it lists all functions) it says error:
We were not able to load some functions in the list due to errors. Refresh the page to try again.

Looking at the deployment center logs, I see:
Function triggers synchronization failed due to Response status code does not indicate success: 500 (Internal Server Error).. Please run sync trigger manually.

In app insights I see this ArgumentException. Which could at some point have been correct, I might have deployed a version of the app with duplicate function names. But now that is fixed, still no joy. I even tried removing the ping function entirely, but that does not work either:

System.ArgumentException: An item with the same key has already been added. Key: Ping

Stack trace:
System.ArgumentException: at System.ThrowHelper.ThrowAddingDuplicateWithKeyArgumentException (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e) at System.Collections.Generic.Dictionary`2.TryInsert (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e) at System.Collections.Generic.Dictionary`2.Add (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e) at System.Linq.Enumerable.ToDictionary (System.Linq, Version=8.0.0.0, Culture=neutral, PublicKeyToken=b03f5f7f11d50a3a) at Microsoft.Azure.WebJobs.Script.WebHost.StartupContextProvider.GetFunctionSecretsOrNull (Microsoft.Azure.WebJobs.Script.WebHost, Version=4.1040.0.0, Culture=neutral, PublicKeyToken=null: /_/src/WebJobs.Script.WebHost/StartupContextProvider.cs:86) at Microsoft.Azure.WebJobs.Script.WebHost.SecretManager.InitializeCache (Microsoft.Azure.WebJobs.Script.WebHost, Version=4.1040.0.0, Culture=neutral, PublicKeyToken=null: /_/src/WebJobs.Script.WebHost/Security/KeyManagement/SecretManager.cs:872) at Microsoft.Azure.WebJobs.Script.WebHost.DefaultSecretManagerProvider.Create (Microsoft.Azure.WebJobs.Script.WebHost, Version=4.1040.0.0, Culture=neutral, PublicKeyToken=null: /_/src/WebJobs.Script.WebHost/Security/KeyManagement/DefaultSecretManagerProvider.cs:77) at System.Lazy`1.ViaFactory (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e) at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e) at System.Lazy`1.CreateValue (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e) at Microsoft.Azure.WebJobs.Script.WebHost.Management.FunctionsSyncManager.PrepareSyncTriggers (Microsoft.Azure.WebJobs.Script.WebHost, Version=4.1040.0.0, Culture=neutral, PublicKeyToken=null: /_/src/WebJobs.Script.WebHost/Management/FunctionsSyncManager.cs:189) at Microsoft.Azure.WebJobs.Script.WebHost.Management.FunctionsSyncManager+<GetSyncTriggersPayload>d__39.MoveNext (Microsoft.Azure.WebJobs.Script.WebHost, Version=4.1040.0.0, Culture=neutral, PublicKeyToken=null: /_/src/WebJobs.Script.WebHost/Management/FunctionsSyncManager.cs:309) at System.Runtime.ExceptionServices.ExceptionDispatchInfo.Throw (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e) at System.Runtime.CompilerServices.TaskAwaiter.ThrowForNonSuccess (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e) at System.Runtime.CompilerServices.TaskAwaiter.HandleNonSuccessAndDebuggerNotification (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e) at System.Runtime.CompilerServices.TaskAwaiter`1.GetResult (System.Private.CoreLib, Version=8.0.0.0, Culture=neutral, PublicKeyToken=7cec85d7bea7798e) at Microsoft.Azure.WebJobs.Script.WebHost.Management.FunctionsSyncManager+<TrySyncTriggersAsync>d__33.MoveNext (Microsoft.Azure.WebJobs.Script.WebHost, Version=4.1040.0.0, Culture=neutral, PublicKeyToken=null: /_/src/WebJobs.Script.WebHost/Management/FunctionsSyncManager.cs:123)

Tried restarting the app, deploying another build, does not work. No kudu access either since this is flex.

This means I don't see my new triggers I have added, this is a real blocker. Any feedback appreciated.