I’ve also been pulling my hair out with this exact issue, following the same tutorial. Unfortunately, opening via Ctrl + F5 does not fix it for me.
At this point, I’m thinking that there must be some issue with the sample assets included in the Arena Shooter template, as I can create a new blank project and successfully create a C++ class, compile, and derive a blueprint class from it, and have that continue to function after closing and re-opening. Following the same steps with the Arena Shooter template immediately gives me broken files, with the same error shown in the OP.
I’ve tried disabling Live Coding and Hot Reload, deleting Binaries/Intermediate/.sln and rebuilding, ensured I have all the correct VS dependencies installed (following the Setting Up Visual Studio page in the documentation), installed additional versions of MSVC, verified UE install, uninstalled VS completely and switched to VSCode (same result where only blank projects work), uninstalled that and started over with a fresh VS install.