ASP.Net MVC and MVC Core Error 500 after editing cshtml Razor page

I’ve had this pop up a few times over the years when editing razor synctax cshtml files. There is some perfectly legal c# code that even compiles fine in your razor files, but will fail when you try to run it- specifcally, when you do this in c#:

if(condition == true)
something = somethingelse;

Perfectly legal to do a single line of code following a conditional statement. However, when this is run inside a code block in a razor/cshtml file, it will fail! So you always have to enclose your code block in enclosing braces like so:
if(condition == true)
something = somethingelse;

I feel like this was overlooked in razor version 0.1 or something and was never corrected later. It would be nice if it at least failed during compile time.

System.Threading.Tasks.Task`1[Microsoft.AspNet.Mvc.Rendering.HtmlString] in place of Html.PartialAsync

System.Threading.Tasks.Task`1[Microsoft.AspNet.Mvc.Rendering.HtmlString] showed in my cshtml page where partial views were supposed to render. This was after upgrading to core 3.1 and going through the warnings that said Html.Partial should be replaced with Html.PartialAsync now to prevent deadlocks. Great, I’ll just go replace them all… blindly, because that’s how I roll.
This resulted in the System.Threading.Tasks.Task`1[Microsoft.AspNet.Mvc.Rendering.HtmlString] appearing in the page – what the.
So you actually need to add await to the code when changing to the PartialAsync – so your call would look like this now:

@async Html.PartialAsync()

instead of the old way: