After migration from .NET core 2.2 to .NET 5 the application won't start after deploying to azure app service - startup timeout

Question

I am having the following problem. A while ago I migrated my project from .net core 2.2 to .net 5. Migration itself was no problem, locally everything worked almost out of the box. But then I was facing problems deploying the app into an azure app service. The app wouldn't start up. I was getting start up timeouts. After a while I solved the problem by switching the hosting model to outOfProcess

<PropertyGroup>
  <AspNetCoreHostingModel>OutOfProcess</AspNetCoreHostingModel>
</PropertyGroup>

Because of lack of time to thoroughly test the application, I had to stick with .net 2.2 until now.

Now that I migrated again, I am facing the same issue. Locally everything works just fine, but after deploying to the app service, the application won't start. But the hostingModel doesn't solve it this time.

I tried linux and windows app service, and I tried to deploy via our azure devops pipes as well as manually from VS. I tried to deploy into an existing app service, I tried to deploy into a new app service, created during the deployment process. None of it solves it.

When i look at the log stream, I see the following:

2022-02-10T09:13:55.360Z ERROR - Container webapp... for site t2bwebappdev did not start within expected time limit. Elapsed time = 230.2593377 sec 2022-02-10T09:13:55.368Z ERROR - Container webapp... didn't respond to HTTP pings on port: 8080, failing site start. See container logs for debugging.

So I tried to solve this via PORTS and WEBSITES_PORT settings - but non of it seems to get it up and runnig.

Thanks in advance for any hints on how to solve this.

Update:

While I was playing around with the logs, I saw that the app was listening on port 5000. Seems with the Net5 upgrade the launchsettings.json is being ignored.

Then I just dockerized it from VS 2019, and in that container I can also not reach the app. So after all this, could it just be a port issue?