Puzzled

I have something of a puzzle at Day Job, one that is drawing far too much of my time and brainpower.  A closed-source web application we use suddenly began performing about fifty times slower than normal, under practically no load (i.e. one user).  We've already tested network latency and bandwidth, and the responsiveness of the underlying database.  Everything appears fine.  Every other instance of the web application, running on other servers, works fine.  There were supposedly no OS updates pushed to the server.  But now that commercial web application is performing fifty times slower.  The home-grown web applications hosted on the same server are performing normally.  And neither our data center team nor the vendor have a clue.  Alas, I'm expected to solve, or coordinate the solution of, this problem.  Yay.  Go, me!  So rather than a longer blog post, I shall merely wish everybody well and get to bed so I can face the world bright eyed and bushy tailed in morning, and resume tackling the problem.  Goodnight and best wishes, world!