I can't reproduce any problem using that minimal project (note it does not specify an app ID, so I just put in 480). It correctly launches and gets the persona name and displays it with no error messages and nothing unusual in the browser console.
It's a really weird problem that you've described: the Steamworks plugin always obtains the persona name from the Steamworks SDK on startup, regardless of whether your events refer to it. Then when you use the PersonaName expression it just returns the string it obtained on startup. So I cannot imagine under what circumstances it would only fail when using that expression, nor how it could have anything to do with the "missing executable" error, because using that expression just returns a string in JavaScript like any other expression.
My best guess without knowing more is some DLL files have been mixed up. The Steamworks plugin bundles its own DLLs, so if you are trying to do something like copy DLL files like you used to have to with Greenworks, you'll might actually just paste in the wrong DLL and make it crash. Using Steamworks is much simpler - refer to the addon documentation and make sure you are only doing that, and aren't doing other steps that you don't really need.
Other than that my best guess is something has got corrupted. Try saving a copy of the project that does not work, and start over: uninstall everything, reinstall everything again being careful to get the latest version of everything - possibly on a new system entirely - and try again. If it works, you could use a diff tool like WinMerge to compare the working version to the broken version and see what the changes are (e.g. maybe a DLL file is different). If they're identical, it would mean something else on the system was wrong - perhaps a corrupt Steam install or something.