ASP.NET Web Forms was Microsoft's dominant web framework through the 2000s, built around a page lifecycle, server controls and ViewState. A large number of enterprise intranets and portals still run on it, usually accumulating years of feature additions on top of an architecture nobody remaining fully understands.
Signs your ASP.NET Web Forms system needs a specialist, not a generalist.
Migrate the application page by page to ASP.NET MVC or a modern front end, while the rest of the Web Forms app keeps running underneath.
Tell us what's going on — most first conversations take fifteen minutes.