Designing a web application's UX/UI is always a beast.
When you're designing websites, you should start with the content.
When you're designing for web apps, the content is often data or the result of data analysis. Even a small snippet of data that is unaccounted for, can be enough to sink a UI.
On a recent project involving the design of an optimization feature, there are multiple moving pieces. You have data scientists, developers, product managers, and of course me, the UX/UI designer.
During an agile sprint, the designer is prototyping, wireframing, etc. The data scientists are constantly changing and tweaking the algorithm. The product manager is doing a million things. After several weeks, the UI was coming to a close.
And of course, there was a variable that we did not account for. The engineers hadn't gotten to the part where they were working with the API for that data, so no one talked about it that frequently. Of course, it's never just one piece of data.
It was the most complicated piece of data, stretching the limits of the current UI, to the point of breaking it.
Of course, there wasn't much to worry about. You just have to go back to the drawing board, add another constraint, and come up with an even better solution.
Don't forget. Content first. Data first.