I work on a project meant to sell a service and meant to manage the service being sold to the consumer. However, the button to actually buy the service is hidden by a scroll bar on all but the widest of screens. Unless you scroll the widget or have a 22 inch monitor, you will not see the purchase button.
Why? The UI was designed in on a wide screen and we developers are just the implementers of the picture. UI is quite often taken from a drawing and little else. It looks great in a mockup, but it isn't all that practical.
> UI is quite often taken from a drawing and little else
The way I've solved this these days when working with people who aren't familiar with responsive design (older/inexperienced designers or clients directly) is to print them an A3 page with outlines of a vertical phone and tablet and a horizontal desktop screen, vaguely to scale, and all including a "below the fold area", and tell them to draw on that. This almost always gives me enough information to implement a properly responsive design.
It drives me crazy that even though huge, wide computer screens are completely ubiquitous, there seems to be a whole generation of UX designers that only ever use (and therefore only ever develop) full-screen applications.
It's like they learned to compute on an iPad and then use the same mental model for every other device they encounter.
UX designers are appealing to their customer, who wants to see something which is very pretty on the big screen they use to present their work. They get paid for wow during the presentation, not for anything else.
A friend of mine hired a UX designer for her startup and the entire main page will soon look like a beautiful poster. But it is utterly horrendous on mobile, which is where 60% of the traffic is.
Not to mention that it is now littered with images that are going to make page load times horrible.
At least there was a scrollbar... one of the worst UI disasters I've encountered involves a truly horrible LMS by a trendy startup where most of a class of ~100 students couldn't log in on the first day, because the button was in the top right corner of a gigantic fixed-width overflow:hidden element. There were a bunch of other huge fuckups, not just in the UI...
I don't remember the name, but oddly enough I do remember that it was Canadian, and the company was very short-lived. It was around the time SPAs started becoming trendy (near the start of the last deecade), and I remember the multiple-minute load times, dozens of MB transferred, and the insane CPU usage, along with all the other horrible usability issues it had.
Why? The UI was designed in on a wide screen and we developers are just the implementers of the picture. UI is quite often taken from a drawing and little else. It looks great in a mockup, but it isn't all that practical.