VS2019 F5 debug breakpoints don't hit

Basic function app template doesn't F5 debug in VS2019.

I have just started to develop a function so following the docs here: https://docs.microsoft.com/en-us/azure/azure-functions/functions-develop-vs but with VS2019.

I created the basic function with http trigger. Without then changing any code I tried F5 to debug it however none of my breakpoints are hit. If I cancel and try to reenable the breakpoint during the debug then I'm told "no symbols have been loaded for this document".

If I close the solution and open the exact same code in VS2017 and hit F5 then it does attach correctly and the debugger hits my breakpoints.

What is the difference between these two? I don't want to have to attach a debugger manually each time as I can't step the startup code.

Target Framework .NET Core 2.1
Azure Functions Core Tools 2.7.1633
Function Runtime Version: 2.0.12673.0
VS Enterprise 2019 v16.2.5 and v16.3.2
OS: Microsoft Windows 10 Enterprise 10.0.17763