I signed up just for this thread, and to echo similar feedback.
We have one S5 onsite, and were taken by surprise when half the web interface suddenly disappeared. Hoping this was a firmware glitch, we tried to be patient, and waited for a future release to put things back. After updating to 8.1.3.0 and seeing no changes, I went searching for answers, which led me here.
The old web interface functionality was extremely useful to our workflow. We used it to log and schedule maintenance tasks, track print completion rate, and record material type usage, to name just a few. The S5 exists only on our LAN, behind a firewall, with no plans to use any cloud functionality. I imagine we're far from the only company with this setup.
What was the logic of removing these features from the web interface? Even if they're available somewhere else, having all maintenance information available to everyone on the LAN without needing special accounts, access, or software was extremely valuable. I'm not going to be hyperbolic and say we're going to toss the printer out over this, but it's definitely disappointing and frustrating to see features disappear from any product, and especially after you already bought it.